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Asked: 2026-05-25T19:27:26+00:00

I’m working on a PHP application that needs to obtain data from a topographical

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I’m working on a PHP application that needs to obtain data from a topographical map (different elevations denoted by different colors). I need to do two things:

  1. Using this map (800×600), find a way to determine the exact pixel location of a particular city. For example, San Francisco is located at precisely 121×585.

  2. Using the location from (1) above, I need to read the exact color at that location.

Note: The map provider does not provide location-based data, only a colored map. I suspect multiple libraries would be needed to map coordinates to locations on the map (via a ratio?) and then use OCR to read the color.

Are there any PHP libraries/tools that do this? How would you pull this off?

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  1. Editorial Team

    Once you know the pixel-coordinates, you can use PHP’s built-in GD library to sample the color of an arbitrary pixel quite easily.

    The tricky bit will be determining the pixel to sample, which can get pretty darned tricky. The earth being sphere-like, maps use various projections to produce a 2-d representation. If you know how the colored map image is projected, and you know the latitude/longitude of the pixel at (0,0), you should be able to write a function to convert lat/long to a pixel coordinate.

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