Each map that you introduce into GPSS must have two accurate points, one toward the Northeast (top left) and one toward the Southwest (bottom left).
This allows GPSS to calculate all other points on the map.
It's best to pick a map with a defined feature close to the NE corner and another feature close to the SW unless...
| · | you have a special need to develop maps of a specific scale
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| · | can work using a handheld GPS unit with readout (and plenty of time to drive from your NE point to your SW point) and thus can find exact locations without using towns, landmarks or other mapped features
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| · | you are working with software that has a locator readout that you can copy
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If you're copying maps from software, it's usually easy enough to zoom in or out or cut out a section that makes this easy.
After picking your points and writing down their locations, the rest of the procedure is explained in The BMP File.
Example (caution, numerical translation of lat/long)
For example, you might more or less randomly begin with this area:
But, unless you have a GPS unit and a four-wheel drive vehicle, you're not going to find latitude & longitude here.
Better to start with 2 locations you could look up on a gazetteer:
Here, Gilchrist is toward the NE and Naubinway toward the SW (though the latter is not ideal, being an appreciable distance from the SW corner - but this is a sparsely-settled area, and we couldn't get the two population centers to be closer to the edges of a 640 x 480 screen capture.)
Gilchrist, we find from the United States Geological Survey