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.
Although the process takes a little time it’s well worth the result. For practically any field of study, this process can be used to accurately identify where two variables intersect, allowing you to identify your region of interest for overlay with other informative maps in Surfer.
Surfer does not support the creation of standard legends for contour maps so the legend at the bottom of this map was created using drawn rectangle and text objects. The colorscale to the right of the map is the type of legend that is supported in Surfer.
Ok, thanks Katie. Is it possible to overlay more than two maps, maybe three or four? Trying to produce a groundwater potential map.
Hi Leo. Yes, it is possible to overlay more than two maps in Surfer. In fact, to my knowledge there is not a limit on the number of maps that can be overlaid in Surfer.
Very strange, looks like the website is trying to parse the formula as per html code.
Once last try,:
IF(A>50,1,0)*IF(B the data based on the user defined parameters, rather than manually adjusting contour lines.
If the grid files are different geometries that I expect that you can use intermediate steps to create interpolated grid files with the same geometry in order to apply the above approach.
Not sure what happened above. (plus clearer explanation).
Correct formula would be:
IF(A>50,1,0)*IF(Bg the two grids together a new grid is created with a value of 1 where the two previous grids are 1, and 0 elsewhere.
Another, (much) quicker approach could be:
If rainfall is Grid A and Temp is Grid B:
1: Use the following formula in grid math: IF(A>50,1,0)*IF(Brid with a 1 value only where both of these conditions are true, 0 else.
2: Plot the resulting grid as a contour plot using the advanced method above.
This assumes the two grids share the same geometry. Done in Surfer 10.
Computed in Surfer 10. This requires both the grids to be the same geometry.