 Extracting information from contour maps is a really valuable skill. You'll see contour maps on TV weathercasts and on weather websites and mobile apps, so it's very helpful to be able to gather some information from them, and I'm going to show you some examples of how to interpret contour maps. This is a map of surface temperature at 19z on Thursday, May 18, 2017. If we do the time conversion, that's 3pm Eastern daylight time, so this map comes from mid-afternoon in the eastern US. Along the west coast, it was noon. On this map of afternoon temperatures, we can see that it was really warm from mid-May in the east. Using the pattern of isotherms, we can estimate the actual temperatures anywhere on the map. The first step is always to determine your contour interval, and here it's 5 degrees Fahrenheit. We see an 85 degree isotherm running through Pennsylvania. All along that isotherm, the temperature is 85 degrees, and immediately to its east is a 90 degree isotherm. Along that isotherm, the temperature is 90 degrees, so each isotherm represents a change of 5 degrees compared to the isotherm that it's adjacent to. Knowing that, we can estimate the temperature anywhere on the map. If we picked a spot here in central Pennsylvania, we know the temperature is between 85 and 90 degrees because it falls between those two contours. Anywhere inside this 90 degree isotherm, the temperature is greater than 90 degrees, but we know it's less than 95 degrees because there is no 95 degree isotherm drawn. For a different challenge, we could pick a spot in western North Carolina. What's the temperature here? It looks like it lies between two 85 degree isotherms, but if we look way back to the west, we see this 80 degree isotherm running through the Midwest. So temperatures in western North Carolina are greater than 80 degrees, but less than 85 degrees. If we change to a map of sea level pressure in millibars, here we don't have the color coding, but the process is the same. Once we determine our contour interval, we're all set, and it looks like it's four millibars here. Since we have a 1004 millibar isobar here in Texas, immediately adjacent to a 1008 millibar isobar. So if we wanted to know the pressure near the center of low pressure in Texas, we know that it's less than 1004 millibars. The values of isobars are decreasing as you get closer to the low from 1008 here to 1004 here, but we know that the pressure is also greater than 1000 millibars since there is no 1000 millibar isobar drawn. So the pressure here is between 1000 and 1004 millibars. Here in Missouri, we have another one of those cases where it looks like it's between contours with the same value. 1012 millibars here to the northwest and 1012 millibars to the southeast. But if we look here to the southwest and the northeast, we have 1008 millibar isobars. So we know the pressure at our point in Missouri is greater than 1008 millibars, but less than 10012 millibars. So always start by identifying your contour interval and study values of the contours near your point to estimate a range of values.