I communicated with a user recently who wanted to find the area of overlap of one specific contour line on one contour map with a specific contour line on another contour map. In his case the first contour map was temperature and the second was rainfall. He wanted to find the area where temperature was above one value and rainfall was above another value. Whether this was for agriculture or for some other purpose I’m not sure, but it got me thinking that there could be many applications for a use like this. For example, you may have a contour map of density of one endangered species, and another for a second endangered species, and you’re trying to identify high populations of both in order to create a wildlife refuge. Or maybe you have population of people on one contour map and energy use on another, and you want to find areas with low population but high energy usage so you can send conservationists into that area to notify the population of smart practices. The uses are endless!
So that said, below are the steps to determine the area where two specific contour levels on two different maps intersect. In this case, I’ll be finding the area in Colorado where temperature is greater than 12oC and precipitation is less than 50 hundredths of inches, which may indicate an area that is more prone to wildfires. The data used in this article was obtained from NOAA. January 2015 – November 2015 data was averaged and then gridded in order to produce the attached grids.