 Good morning everybody See if you look at the GIS as a field just information system It's a subject by itself. It's a full-fledged subject which can be run as a one semester program or one degree program and all It's very difficult to give justification to the subject within 90 minutes But I'll try my best to give at least an overview and you know from the questions which I saw from yesterday's portions There have been a question even use of remote sensing and GIS for watershed modeling So maybe you know many of you may be familiar with the GIS But for the benefit of other departments, I'll try to give you an overview in as simple as possible But you know one cannot cover a lecture on an overview avoiding theory, but I'll try to make it as simple as possible and of course following this lecture afternoon you will have a demonstration of the GIS package itself and following the demonstration we will show you some of the Applications which have been done using the GIS tool which will be demonstrating in the afternoon Okay, see just before going to the theory the one thing I want to tell See now I have come from a residence to this department to deliver the lecture Naturally when I leave my residence, I'll try to see which is the optimal route through which I should come So that I can come on time for starting the lecture This is my case now you take another case like an agriculture person a farmer is there He would like to cultivate Crop during curry for rabbi season or summer season. He will try to see what crop he should cultivate in that season so that his Profit is reasonable that will depend on what is rainfall Terrain condition land use practices etc. etc Now suppose and person is there on an irrigation department He will try to see when he has to let out water from the reservoir Based on for what land utility is being done. What is that whether there had been a rainfall? Everything seeing that he will try to decide it See there are number of questions which we come across every day for solving many problems If you look at all these questions, what will you see? You will see that all these questions refer to some Geographical processes on the surface of the earth There are number of questions which we come across which we try to solve and everything refers to some geographical Surfaces on the ground some spatial phenomena on the ground. Okay, so Question is easy. We have to solve it So, how do we do even a simple question as I said I need the optimal path to receive reach this place I don't need a shortest path. I need an optimal path So naturally, I will try to see what is the road network how many traffic signals are there Which route I should take may be a longer route, but signals may be less I may have a flyover through which I can come So, you know even to solve any simple question, which is of spatial in nature You have to collect data from different sources Integrate them and then analyze them. Isn't it because it's daily problem, which we try to see So to do this to solve these kinds of problems, which are spatial based That technology of GIS comes into picture GIS if you really want to define it can be considered art science engineering or technology Because I won't consider GIS as completely a geography field I won't consider it's a maths field because see I am from mathematics field I cannot consider that it belongs to pure science Or I cannot say, okay, it's only an engineering It has the technology also which gets involved So the art or science or engineering or discipline Which tries to solve you these kinds of problems is the GIS technology Okay, so now you know this particular GIS discipline started generating Massive interest worldwide. In fact, if you look at it today, there is no field where GIS cannot be applied That is the way this technology is growing. It's not only cell engineering or elemental people or geology people Any planning any management? Everybody wants to use this field And you know, especially along with the technology of remote sensing this GIS started growing Because you know the benefits which came from handling remote sensing data Computer science field everything got Incorporated into this interdisciplinary area Okay, so during over the last in fact, you know, I started working during 80s and today every day this technology is growing Okay, during last three decades, there have been a very rapid Rate of improvement development, etc. The theory side technology side application side organization side Implementation side, etc, etc Okay, and as I said, it doesn't belong to one discipline or technology or art or science It is 100% an interdisciplinary area. In fact, if you come to my department, I'll tell I'm from completely a mathematics background person from this institute My team consists of people from computer science electrical engineering physics Geography like, you know, it's a heterogeneous group which works. So GIS is a An interdisciplinary area which covers people from Computer science, mathematics, civil engineering, economics, agriculture, etc, etc Okay, and overall if you try to look at GIS technology broadly we can categorize into three parts one is Hardware and software because you know, it is not that GIS is new conventionally people would have also used Sensories back those days also people have taken massive decisions But you know, they would have used a manual approach Today we are all in the digital technology. Okay, so naturally when you think of digital field hardware is needed And the tool is needed, which is the software. So when you try to broadly categorize GIS One is hardware and software. Next is what for that software is Naturally, you are going to pull the data put it and process it So information processing and what for you are processing the information naturally to apply for something So when you categorize GIS you can broadly put it as hardware and software information processing And then applications Okay, we said information processing the title itself says Geographic information system. So we should know what is an information So what is an information? Think see I give you a number. I say, okay, I'm working in IIT I say my number is two five seven two something one two three seven. I tell If I just give a number two five seven two one two three seven, does it mean anything? It is just a value Your number moment. I say it is the telephone number of so-and-so The same data becomes what? Now any information So information is derived from the interpretation of data Which are symbolic representations of the features, but you know, whenever we say information We have to see the value of the information See suppose I work in an area where I get data three decades back Today every day, you know, suppose you go to an urban area every day the city is growing every day There is a change. Okay. Suppose somebody gives me three decades old data. He may even give me freely the data Will it be useful to me unless you are working the temporal changes? What was there? What is today? Other than that, you know, you want to do some planning as of today. You need the data as of today So the value of information will depend on its timeliness The context in which it is applied. See, suppose I am working on water resources application Somebody gives me, you know, a lot of demographic data Probably a few parameters I may use may not be other information So the value also will depends on the context in which it's applied And you know, I may have data. I may have information, et cetera. If I put it in my cupboard in a file Can I access it whenever I need it? So what happens? It depends on the storage Manipulation and presentation. It should be easily accessible. It should be easily Processible it should be represented the way the user needs Okay, so information is an asset. It is power today It can be bought and sold for prices. That is the way today information is there But this information When you try to represent in the form in such a way Users can analyze it, manipulate it, process it and represent it There comes the information system Okay, from data we came information from information then naturally information system comes into picture Then when you say information system, if you see the theory broadly we can define Divide into two major categories One is called as transaction processing system Other is called decision support system What is transaction processing system? You go to banks today, you know, everything is computerized whether you go to bank Or whether you go to railways Either you go for airline booking everything, you know, you just give he will see and you know if your PNR moves off He says okay, you're moved up. Your reservation is confirmed Everything is online. You go to bank. You put money. It gets credited. You take money. It gets debited Everything is what happens There the occurrence occurs As per the way it is happening That is a clear cut rule in Updation and the method they have to follow So, you know, there it works in such a way Updation can be done in a clear cut procedure Whenever you go to the place like airlines or railways or banks So those kind of Processing or the information system we call it as transaction Processing system So it is very easy. There is no, you know extra modeling or thinking or anything well defined rules are followed The other thing is a decision support system here. What we try to do here emphasis is on analysis modeling Manipulation, etc. So that the data can be used finally to an end user So here what happens the same information system becomes a decision support system So geographic information system is a dss The heart of gis is It's manipulation and analysis Okay, the more powerful it is in analysis the usefulness increases Okay, geographic information system is an information system in the category of a dss In fact, you know gis we call it as a spatial decision support system So a geographic information system is a tool Which can accept large volumes of Spatial data that's a place where it differs from other Types of databases and information systems large volumes of spatial data derived from variety of sources Retrieve, manipulate, analyze, etc. And display them according to user defined specification Why people are working more and more on gis as I said see suppose there is one Integrated gis for an area like let me take our own city Mumbai city All data let us say our Municipal Corporation of Greater Mumbai. They have all data. Let us ask It will not be useful only for them. Everybody can use the same data for his Application as far as utility is concerned Decision is concerned planning is concerned. So, you know once you form a gis for an application It can help several users and it can display the result according to his application That's why and display them according to user defined Specifications and of course whenever we talk about gis one has to keep in picture that gis has got both spatial data as well as Attribute data we call non spatial data. We call as spatial data Attribute data and all see suppose I have the village boundaries. Let us take our ward boundary of Mumbai If I just put a map nicely with the ward boundary Will it be alone useful? It will be a showpiece Moment I have to attach it how many people are living in the ward How many facilities are there? It may be in terms of school. It may be in terms of hospitals It may be in terms of banks How many school going children are there all data have to be added to that Boundary so that a planner can use it. So gis has both spatial data and supported Attribute data Why this you know gis is it's of course, it's very useful But you know if you really look at deeper why it becomes very very useful the thing is You cannot see any event occurring across the world without a spatial reference. You take a newspaper in the morning New Delhi comma Mumbai comma comma like that. They write the news See any event occurs. It is Spatial in nature Nothing happens without giving even this class is happening in this room We say moment CEP course means comma comma in this room in this building IIT Bombay. We write it So if you really see everything is spatial in nature and gis is a technology which handles this spatial data So that is why it's usefulness and power increases every day And if you really look at its applications gis can be applied in every work of life Whether you are working for transportation engineering or for a canal alignment problem Or locating a place where you can put a minor irrigation done In each case on each every type of application this technology can be used Okay, but whenever we say spatial data Very easy to tell spatial data But the problems follow because spatial data is not as easy to handle as you handle the other game It is always spatial in nature The reason is the data is Multidimensional how it is multidimensional We have x we have y I have to refer a position wherever I need I have to refer the height correct three and then I have to refer that time If I have to store methodological data naturally last year rainfall this year rainfall or last month rainfall this month rainfall So it has it is basically multidimensional nature. It has to cover x y z and time Based on of course the application, okay And the data is voluminous voluminous that to today's technology if you take You are all seeing you know, we all see this google earth. We see the map. We see the images Today in what resolution we are working In fact the image data which they are putting is all of us know 0.6 Meter resolution and they have launched a new satellite with 0.5 meter resolution So, you know spatial data when you say it is voluminous in nature It's not like those days you take a 50,000 scale toposheet or a map Work everything and finalize when you are in the digital platform. See those days we were happy with the 10 mb drive Today even 160 gb drive. We are not happy That is the level, you know storage capacity is increasing the amount of data handling is increasing The amount of data flowing is also increasing. Okay, spatial Data nature is multidimensional voluminous And whenever we talk about the map data surface data earth data, etc Another major problem is That we are Not on a flat ground We are on an ellipsoidal surface So the projection comes into picture. You see if I work only within the iIT campus I can treat it as a flat terrain. I don't need any projection But suppose I work for the whole state The area of coverage is more Naturally the data has to be projected on a Flat paper to work on a digital. I cannot Scan a globe inside the computer. I had to only put a map and scan it. Okay So projection comes into picture the way of analysis methods modeling everything changes Because you know a person because I saw the course title as soft computing See a person who is working on hydrology may integrate some model Person who is working on agriculture may enter another model So, you know it needs unique analysis that has to be handled And you know as I said even in the beginning your GIS means you have to integrate data from different sources See when I work on an application you go to different agency collect data All data may not be readily in the form you need it All may not be in the same projection you need it all may not be in the same scale you need it And some may be in tabular form some may be in map form some may be in image form So, you know you need to integrate data from multi resources and also Data updation is very expensive as I said, you know information is The timeliness is very essential. So one has to go on update the data, which is a time consuming process And whenever you want in the digital field you say, okay, I get a query I put a query system should give me the answer immediately Okay, so the thing is if I look at really the spatial data It is special in each other or some GIS books, which talk one full chapter only the characteristics of spatial data Why you know so difficult to handle and what are the speciality in the this spatial data Okay, so when this tool handles overall GIS is a software tool Don't assume, you know it gives along with the database you buy the software tool You have to add the database which will be the Back end of the GIS is it so you buy a software tool a GIS tool You add your databases or data sets which you contain and look at evaluate look at spatial data You have to look at GIS Of course, you know this room is not a Cubite it's of its own shape. You consider us a cuboid like we have our rooms One over the other you put the layers. So GIS has to be looked at sir You buy it with a cuboid with the layers of maps Why I'm telling is you have to look at as a container with a layer of maps The reason is whenever you do an analysis in GIS Even though you pull the data from different sources What you have to keep in mind is All data must sit One over the other You have to do pre-processing in the data in such a way If you are covering for the city of Mumbai or maybe let me say for the campus of IIT every map should sit one over the other So when you are really doing processing in GIS All must be of the Same projection and same resolution I cannot handle 25,000 scale data with the 10,000 scale data You have to do a pre-processing in the GIS in such a way finally during Analysis the data layers sit one over the other Okay, so it is the container of maps and beauty is never you try to analyze it Using the data using the proper methods then it becomes a sds It becomes a spatial decision support system. So GIS is see network of hardware software data We people on the procedures Okay, and it started during as I said around last three decades. There is a rapid growth It's see if you look at GIS the first best application if you look at the history of GIS book The one is the application which was done by the canadian government CG is that was the first thing which they said canadian geographic information system They wanted to use computer for just mapping the land inventory Those days we had mainframe systems like IBM systems. They made an attempt to take the data See remote sensing was parallely growing 1972 was the reason that first unmanned civilian satellite was launched But during 60s computers started coming So that you know they thought why not we use the digital world to Store the map data and try to use it at least keeping for an inventory That is the way it started and you know then started growing in 72 landsat satellite the first civilian use satellite was launched by US government and you know The if you look at you see that's a beautiful book on history of GIS Where how we grew every year they are put Okay, so the thing is there was a laboratory in Howard laboratory of computer graphics Where many many people who passed up from that lab? They opened the GIS software companies including the person who is the president of He also passed up from that and he opened that company. So that is the way it started that Became as a start from which it started growing naturally during 80s park info came may Intergraph came many GIS packages started coming We all use the book professor pa borrows book of GIS that was the first book which came as a book now today, you know Daily books are coming hundreds and hundreds of books are there software is that Tools are available uses are millions that is the way it has grown and especially if you look at you know after 2000 We are all captured by WWW we know nothing without web So GIS also has molded itself for it See it has been quick enough to adopt this technology of web based because he when he showed the question of yesterday First two questions were on web isam today. You know nothing is there without web Okay, so even in GIS it's not only the desktop solution People try to put the whole GIS tool so that sitting anywhere in a browser You can do the query you can do the analysis Data may lie somewhere analysis tool may lie somewhere You may be sitting somewhere in any part of the world. You can analyze it So even you know GIS has been quick enough to adopt this web based technology the advantage is See to implement a web based server is expensive difficult put the data But for users it became Easy to use and cheaper See whenever you try to use, you know, there are some websites in india Which stores data even on a web based GIS example is census department NIC you go there are you can take the data query it and get the result They would have spent a lot of money to build it as a user. You don't need to spend any money You query it and get the answer So, you know that moment that web based GIS started coming and people started using internet technology The number of users had grown into millions and millions and every day it's growing Okay Now we saw that, you know, it's a spatial information system and spatial data Now, let us see what is this space because it is handling the spatial data. Let us see the definition of space Space is defined as a relation on a set of objects. Just see the fundamental definition is Space is defined as a relation on a set of objects I am here. You are there. I am an object. You are an object. I say I am in front of you So we define our positions in relations with our positions Isn't it? So the general definition is it is defined as a relation on a set of objects Okay So spatial objects are entities. How do they define them? If I say so and so immediately I will not only Put his position. I will say his name Maybe his qualification etc. He is a participant of this course that will come into picture So the spatial objects are entities are defined as a set of locations Together with the set of attributes or properties characterizing these locations So what we know what is spatial objects? Okay, then I said the relations one thing whenever you work in GIS one has to keep in mind is say normally in geometry what we say We work on Euclidean geometry So we say the distance between you and me I can calculate If we are three people we can calculate the distance among our three uppers. There is no problem It's well defined and in a triangle what we say some of the two sides is always greater than the Third side. These are all well defined geometry. So they are all what metric distances which we follow But in GIS when you come It may not always hold this metric distances theory That you have to keep in mind. It is not that you know, it doesn't follow geometry. It follows fully geometry But based on the applications like I say I put you know, I'm in the road network I have to reach this part instead of reaching this part. I may go that way and come here The reason may be what there may be many traffic jams, which I have to avoid So instead of going this way, I may go to the other place and then go So, you know, one has to keep in mind whenever based on the application you are working on GIS Non metric spaces may arise when distances are need not be symmetric. So when I have to go to A to B Maybe when I'm coming B to A, I can come this way. There may not be any hindrance But when I go to A to B, I'm taking a round route. So A to B need not be equivalent to B to A based on the application So one has to keep in mind when they are handling as far as the spatial distances are concerned Okay, so when we say the space and we want to put all those spatial objects into the GIS or into the Spatial database in a GIS too. So what type of objects we come across? We come across objects which are really nature Like this building, the building has a structure I can take a GPS move around this jeep building and get the boundary of this building Exactly even in terms of latron Okay, so I have Buildings, lakes, water bodies which are really existing True objects and there may be objects which may not exist which you assume and do it Have you anybody seen the contours existing anywhere? We all study on elevation See may all of you are from water sources. You would have used to push it You see the contours we all assume that contours give us the elevation Anybody has built around the wall around any of the contour? No They are all what fictitious lines Assume to be they take the positions at some of the heights Interpolate it and draw the contours Have you seen latitude, longitude, line or equator? These are all we assume they are there for some reference So whenever we put these spatial objects We cover what types of objects? Digital version of real objects Then digital version of Artificial features and over and above when you handle remote sensing data What you do they try satellite tries to take the images and they do the quantization and give the reflectance value for every pixel So they are also artificial in nature So in this when you put create a spatial database We try to cover all these kinds of objects and try to store. So, you know all objects need not be real That may be objects which do not exist which are assume village boundary Again, you know they have all approximated boundary done by an administrator Which we digitize and store it. Okay. So all these objects we try to store So, what are the components of spatial data? You can just look at it one is I said I'll say he is sitting there his x y position location Okay, second is what? His location and my location I give then comes the relations. So what are the components is? locations The relations and I said location alone will not mean anything all the attributes about that Person or if it is a water body or if it is a building we put about all those things. So location relations attributes and So, what are the major four components of spatial data are? locations relations attributes and the time wherever needed Based on your application you store because you know moment you say time Time can be stored as I said if I take the rainfall today's rainfall yesterday's rainfall day before yesterday's rainfall I can put comma comma comma or I'll say last year annual rainfall this year annual rainfall Or I can say the change in the rainfall pattern Many ways the time can be stored. So based on the application people try to store it So but basically what are the components of spatial data are? Location relations attributes and time. So your GIS must be able to handle all these four types of data And next thing is whenever you are working on GIS one has to keep in my picture is What you are trying to represent or put into a GIS? I give an example of our campus IIT campus. It's a big area Okay, so suppose I am working on an application of IIT alone What I'll do? I'll have a big map. I in fact if you come to my lab, you'll see I have 22 sheets Surveys for this campus and they are given Okay, so the scale in I why I'm working is in a large scale Because I need every building I need every electrical pole every Piece of small land. I need it because I'm working an application for the campus alone Suppose somebody works for the entire Mumbai That IIT Bombay may be a small polygon Agreed. It may be a small unit. They don't bother where this building is there or where CSRE is there It may be just okay. It's an IIT Bombay campus. They may write Same thing somebody works for the entire Maharashtra state Even Mumbai may be a small polygon that IIT cut that may be there may not be there So, you know in which same feature can be represented as a point Can be represented as a polygon can be represented as a unit with many polygons So, you know a spatial object can be represented in multiple ways So again a user has to decide in which scale he is working on what detail he needs it Okay, so same feature can be given in a multiple representation Okay, now what are the objects we have to see it when we define an object? I said point can be an object a polygon can be an object So what we assume when we define an object in a GIS is You have to see We assume There is a homogeneity within that object So I am putting a boundary of what our body I am trying to handle it as a single entity in a GIS So when I put that object I am assuming the whole list with the water See actually if you map a lake Pooram it need not have water It may have muddy land little swamp area and then in the underneath when you go there may be Water But when we treat it as a single entity in a GIS We assume it is a only one entity And one record will be there with a set of attributes Within that entity I cannot say A little mud is there little area of water is there a little swamp area is there. We don't do it So, you know an entity is considered as a single entity Where we assume that need not be homogeneity, but we assume Homogeneity and then store it that also one has to keep in Mind and whenever you store the attributes attributes can be in a single table Attributes can be in multiple tables But reference to the same object Simple cases what villages You go to census department. You will get so much so much of data about that village You may not be able to put all the attributes in a table So what we do, okay education one table health another table demography another table But all these tables belong to that record belong to the same village There should be a link So that when I query show me the villages which have zero school One hospital and you know hundred children going to school It should link all those tables and give you the answer Okay, so the data when you organize it Spatial object is treated as a single entity But the tables can be multiple tables again based on your application So with this little concept of spatial objects, how do we define that put the spatial objects People who are working on GIS will be definitely knowing what way we put it Either points or lines Or polygons Three major categories, but you know today if you go to GIS we are not handling three major Sequence or objects are possible. They're all you know multi-line Multi polygon multi geometry if you go to the latest See, I'm not covering you the latest developments in GIS in this lecture because I have asked me to speak only overview If you go today In GIS what is the standard is? He doesn't sit only with point line and polygon Multi polygon multi line multi points and multi geometry which consists of point line and polygon Okay, that is the way it's has been defined But the basically everything the core is point x comma y With a point naturally, can we not make a line when I go in an ordered form? I get the line Then when I start here and close here the same point I get the polygon So the basic spatial objects are points lines and polygons over which all those extensions have come today So when in GIS we treat them as to define the dimensions Because you may wonder, why do we define the dimensions? The reason we define the dimensions are totally we are working on geometry So I have to relate I have to query between objects I have to get a solution between objects. So the basic dimensions play an important role Point is always treated as an object with zero dimension In GIS point is treated because It doesn't have a measure no length no breadth, isn't it? Point is treated as zero dimension Line with one dimension area with two in case you work on volume three Okay, so this is the way we define the dimensions So that one has to keep in mind And you know the scale of observation or mapping will affect what might be represented in a GIS This I told you already the same feature can be a point The same feature can be a polygon So based on the resolution you are working scale you are working It can be a zero dimension. It can be on a two dimension Okay, and the relations how do we store the relations? Relations when you see that is an area itself called spatial relations books are available These are available papers are available What do you say how do we relate the objects? I said, you know the dimensions play an important role Because if I take a point If I put point on a line, it is different When I put a point on a polygon, it is different when I take a point and put it in the space It's different because that point is in a three-dimensional object When I put it a point in a polygon, I'm putting the point in a two-dimensional object So when you try to work on the relations for the query Naturally the dimensions play a role and how do we relate those spatial objects? So people there are good standards available to define the spatial relations between the objects Simple thing which is available. I just put a point can be a neighbor to a point A point can lie on a line A point can be a centroid or it can lie A school can be within an avilage It can be within a polygon etc So one can relate the spatial objects That is a standard today followed in GIS All with the latest standards you want to know about it There is something called nine intersection matrix Which had been done very well by a professor in US Which has become a standard which all the latest GIS tools they follow Nine i matrix we call it And all the spatial relations which can exist Between these kinds of objects have been well defined And even standardized So spatial relations come into picture So we saw what is at all the components of spatial data What are the possible spatial entities And what type of relations that may exist Now comes how do we store them Naturally what comes into picture when we store into a digital tool How to model it How do we store because you know when you see with eyes you know everything We immediately we can okay this person is sitting in front of me Or standing in front of me everything we it automatically goes here But when the question of GIS comes we have to put it into the database There comes the data model A data model is essential to represent the spatial data in a spatial database That is what is a spatial model a data model See basically a data model what it gives it gives you the guidelines How do you store your data in such a way You store the entities as well as the relations between the entities So when you look at that data model Broadly two data models are possible Simple again I'm taking you the simplest available the raster and vector models Okay, maybe when somebody covered GIS or he gave an example He would have given you something from a raster or vector I'll try to give you a little bit about both these models So raster is very easy very simple it is nothing It is equivalent to an image data Remote sensing has grown where you have all the remote sensing images in terms of rows and columns It's a matrix N rows by M columns It's a matrix where the values of the reflectance is stored Same concept has been put because whatever is done in image processing can be directly used in GIS So raster is nothing it is only a data in a matrix form Where you take the data put the grids Try to store the data for each grid the value Very very simple very easy to handle which is going So when you look at it raster model divides the entire area into regular grid Of cells in a specific sequence In fact, you know if you look at it There are areas where you know again people work different models instead of putting a square grid People have worked how to put a hexagon These all went on a research level where you know no GIS tool came Grid became very famous because I said image processing handles a grid pattern A pixel pattern from where the theory could be picked up and used in GIS People did research on different kinds of tessellating the terrain But among all of them normal grid became very common and useful So raster model divides the entire area into regular grid of cells And whenever you have a raster if you have a data for an area You cannot leave some cell empty if it is empty at least you have to put a zero value So it's a space filling every cell should have value If you have only five schools that five grids you may put a school number one two three four Remaining cells come say come you will put zero zero Okay, so it is a space filling and very crucial is the resolution or the cell size How finer I go to the cell size how coarser I go to the cell size Coarser you lose information finer your data becomes heavy Isn't it as I said I can handle 0.6 meter resolution of digital globe also We can store handle our own IRS data which was once upon a time you know 23 meter resolution So coarser be possible finer is also possible it based on the detail And how much you know what is your grid size which you want to handle Accordingly the size has to be defined again here also like I told you about spatial entity Within a cell we assume homogeneity Only in single value can be stored in a cell Okay, one cell gives a single value that one has to keep in mind So all variations within the cell is last And one set of cells and associated values form a layer. I have a land use map I can say this is the grid where the values are stored So that you know 10 rows by 10 columns where you have the values you have a land use map So what you don't store row comma column number you put the value in that row comma column number Okay, one one one one two two two three four like that you make it your land use map one means what two means what three means what That is what you try to store Okay, so each cell you try to put a value So raster model tells what occurs at each place one set of cells and associated values Is a layer it can be elevation it can be land use it can be you know Cell category or anything Since those days what we used to do we used to take a map Those days, you know, there was no digitizer or scanner and all we used to have a template of our grid size Put it over the map pick out what is there content in that grid And manually code it and enter through the keyboard Today scanners are available directly you take a map scan it you change the dpi to what level you need So you decide the resolution data is ready for you for processing Okay, so that technology has changed and whenever we use remote sensing directly digital data is available You don't need to worry at all So raster data is readily available Only thing is whenever you use raster data from remote sensing what you have to keep in mind Their projections are different Resolutions are different area of coverage may not be the same You have to do preprocessing georegister them Then only you can bring it as a layer remote sensing data that one has to keep in mind Okay, so And see resolution I said it's very important because we assume homogeneity within a cell And another thing is when you look at a GIS see in remote sensing Normally they give 8 bit value Normally, you know when you take a single band image they give 8 bit value 0 to 255 See nowadays, you know later some of the higher resolution circulates. They give 6 bit value 7 bit value But you know in GIS what can happen is you can have 8 bit value which is what a byte Like 0 to 255 your pixel value can be there But there may be cases where Instead of 8 bit your values may be more Let me take a case. I am trying to handle in the raster model all the villages of Let me say one district of Marasha There may be how many villages there may be thousands of villages Okay, so let me say there are thousand villages in a district in that district Then can I give 1111 for one village two two two for second village like that If I give a raster, what do I do after 255? Number of villages I have is thousand So I may have to handle the case where the number of pixel values Will be greater than 8 bit So in a GIS when you have the raster values, it can be byte It can be integer or it can be float value When float value get it like we say a elevation You take Okay a contour of 640 Next contour of 660 You interpolate in between Will it give you everything round figure When you interpolate point something point something it will write So you may have to handle integers float As well as byte So a great value in a raster can be of These three categories because you know whenever you use a GIS it will ask you In a raster mode if you go it will ask you whether your data is byte or it's a float or an int Again based on your thematic map you have to give this Okay, so that is possible and also Limitation in raster or the oneness homogeneity Whenever a boundary passes between yourself Naturally We compromise Whichever area covers more We give that value to that we can't help it Okay, so these are limitations Of course, you know, I'm not showing you. I'm not going deeper into the theory on raster model. See