 We began this lesson by watching a video about geodesy. The narrator said that geodesists measure the Earth's shape, rotation, and gravitational field, and how these change. The video makes the point that precise positioning is needed for many scientific endeavors, such as monitoring sea level changes, tectonic plate movements, land uplift, and ice sheet and glacier changes. Precise geolocation information is also required for routing emergency vehicles and deliveries, for construction and mining, for precision agriculture, and for many other civil and commercial activities. Geodesy is fundamental to the production of geospatial data insofar as it provides a system of coordinates for the entire planet, as the video put it. In that sense, geodesy has implications for the entire global economy. Recognizing the importance of geodesy and geospatial data, the United Nations formed a Committee on Global Geospatial Information Management in 2011. The committee argues that a globally coordinated approach to geodesy is fundamental to sustainable development. They point out that two or more geospatial datasets will be needed to assess progress on all 17 of the UN's Sustainable Development Goals for 2030. The goals and their associated geospatial datasets are shown in this matrix. In 2015, the United Nations General Assembly affirmed the importance of geodesy and geospatial information in a remarkable and unprecedented resolution. The resolution encourages member nations to adopt a common geodetic reference frame to support consistent, precise positioning worldwide. It also encourages data sharing and international cooperation in building out the world's geodetic infrastructure of the global navigation satellite system and ground-based reference stations. Here's Fiji's ambassador to the UN introducing the resolution to the General Assembly. It's no surprise that Fiji and other small island nations share a concern about the accurate measurement of sea level. This map shows how a sea level rise of just one meter would impact the urbanized southeast corner of Fiji's main island. Sea levels could rise that much by the end of this century, according to the Intergovernmental Panel on Climate Change. At its essence, the global geodetic reference frame is an earth-centered, earth-fixed, three-dimensional coordinate system. Three axes, X, Y, and Z, originate at Earth's center of mass. X and Y are separated by 90 degrees, and both intersect the Earth's equator. The Z-axis aligns with an international reference pole. Earth-fixed means that the X, Y, and Z axes rotate with the Earth. That means that velocities of a position, as well as its X, Y, and Z coordinates, can be specified in the system. The GPS receiver in your smartphone and other devices calculates three-dimensional coordinates from radio signals broadcast by GNSS satellites, including the United States military's global positioning system. But GPS goes one step further. It associates the 3D coordinates with positions on or near an ellipsoid surface that closely approximates Earth's shape. But hang on, what is Earth's shape anyway? Geodesists define the shape of the Earth using mathematical models called geoids. A geoid is a surface that approximates global mean sea level, but across which gravity is everywhere equal. Technically, a geoid is a three-dimensional statistical surface that fits as closely as possible gravity measurements taken at millions of locations around the world. Geoids are lumpy because gravity varies from place to place in response to local differences in terrain and the variations in the density of materials in Earth's interior. Obviously, the lumpiness is exaggerated in this image. Ellipsoids are commonly used as surrogates for geoids. They simplify the mathematics involved in relating a coordinate system grid to a model of the Earth's shape. Now this is important. The relationship between an ellipsoid surface and a coordinate system is called a horizontal datum. The particular datum used by GPS is the World Geodetic System of 1984, or WGS84. Like the global geodetic reference frame I described earlier, the WGS84 datum is Earth-centered. Horizontal positions, east to west and north to south on the ellipsoid, can be specified as latitude and longitude coordinates. As you know, latitudes and longitudes are widely used for navigation, for spatial analysis, and for map projections. GPS calculates vertical positions called heights in relation to the ellipsoid surface. Although it is labeled in Spanish, this diagram clearly illustrates a relationship between the terrain surface and the ellipsoid surface and a geoid surface. Unlike horizontal datums, which are based on ellipsoids, vertical datums are based on geoids. Geoidal heights can be derived from ellipsoidal heights using the formula shown in the illustration. Geospatial professionals should know that both vertical and horizontal datums are changing soon in the U.S. Consistent with the goals of the UN resolution, the U.S. National Geodetic Survey plans to adopt a new global geodetic reference frame in 2022. What geodesists and land surveyors call the realization of a datum is a physical network of control point locations marked by permanent monuments, like the two shown here. The monument on the left is for horizontal positions and the one on the right is for vertical positions. Currently, the latitude and longitude coordinates of horizontal control points in the U.S. are expressed in relation to the North American datum of 1983. NAD83 is to be replaced because it is based on an outdated ellipsoid model that is not precisely Earth-centered. Heights at vertical control points are expressed in relation to the current North American vertical datum of 1988. NAVD88 will be replaced because it too is based on an outdated geoid model of the Earth's shape. Replacing one horizontal datum with another causes a shift in the global grid of latitudes and longitudes. This fact explains in part the discrepancy between the prime meridian at Greenwich and the GPS position recorded at the same location, which indicates a position slightly east of zero degrees longitude. In the past, the National Geodetic Survey accommodated such shifts by adjusting the coordinates of control point monuments like this one. However, NGS plans to quit maintaining its physical control markers after the shift to the global geodetic reference frame. Instead of the existing passive control network, NGS will implement dynamic control through a system of continuously operating reference stations like the one pictured here in Colorado. The adoption of the new reference frame, new horizontal and vertical datums, and a dynamic control strategy will enable the National Geodetic Survey to provide much more accurate coordinates and heights to its users. However, as author and educator and Penn State colleague Jan Van Sickle notes, it will be a big change for land surveyors and GIS professionals who are responsible for creating and integrating geospatial datasets based on different reference frameworks. As an aside, let me say a few words now about map projections. Now, geodesists care about the shape of the actual Earth, not so much its representation on maps. However, geospatial professionals who produce cartographic information products do need to worry about projections. Toward the end of the geodesy video, we watched a three-dimensional globe being flattened into a two-dimensional map. I'm sure you know that map projections are the mathematical equations used to transform latitude and longitude coordinates into plane coordinates. Although digital globes and 3D GIS are increasingly common, map projections still matter. One reason they matter is that many geospatial datasets specify positions in projected plane coordinates, such as universal transverse mercator or UTM coordinates, and, in the U.S., state plane coordinates. For example, consider this conceptual model of a transverse mercator map projection on the left and the resulting map on the right. The thick red line on the globe represents the line of tangency between the globe and the projection surface, which in this case is a cylinder. The thick red line on the map is the standard meridian, along which projection distortion is zero. The red circles on the map reveal that projection distortion increases with distance from the standard line. And in this example, a conceptual model of a Lambert conformal conic projection highlights two lines of tangency between the globe and a conical projection surface. Those lines correspond with the two standard parallels on the map. Red circles on the map confirm that map scale is equal along both standard parallels. Distortion increases with distance from the standard parallels everywhere else in the projected map and in the coordinate system on which the map is based. GIS pros need to understand the characteristics of the transverse mercator and Lambert conic conformal projections upon which those common coordinate systems are based. We also ought to be familiar with the properties, advantages, and disadvantages of the infamous web mercator, the default projection for web mapping applications like Google Maps and ArcGIS Online. This case study and the one that preceded it about GIS and the eradication of polio show why positioning and data acquisition matter to people and organizations of many kinds. The U.S. Department of Labor recognizes positioning and data acquisition as a foundational sector of the geospatial technology industry. The historic United Nations resolution for a global geodetic reference frame highlights the foundational importance of geodesy and the need for precise earth observations to create a more sustainable world. Hey there, everyone. I just wanted to point out something that I noticed in this infographic that I enjoyed. In lesson one, we learned about e-health and their work with the Nigerian government organization in charge of geospatial data. I forget their actual title right now, as well as support from the Bill and Linda Gates Foundation. But they were working on polio and that's this issue here, I would imagine. It didn't seem to fall under any other category. And what they needed to get was these two data sets and they digitized satellite imagery from, I think, World Preview 2. And the thing I wanted to highlight was that they got the basic building block to their problem, but it is literally the same building block that is going to be in every single issue laid out by the GGIM. And so it makes me wonder, what have they done with that sort of data in 2014, I believe it is, and what they're going to do with it in the future. And I just thought that was worth highlighting to you folks. So thank you.