# Scale Lat/Lon maps correctly in Surfer

When maps are displayed based on latitude and longitude coordinates extending over a large region, the map might appear somewhat distorted (stretched in one direction). This occurs because one degree of latitude is not equivalent to one degree of longitude. To re-scale the map, multiply the X scale by the cosine of the central latitude, and enter this as the Y scale.

For example, consider a base map of the state of California (CA2010.GSB, located in the Samples folder by default this is downloaded to C:\Program Files\Golden Software\Surfer\Samples).

At the default scale, the map of California in Lat/Lon coordinates looks stretched in the horizontal direction.

1. Determine the latitude for the parallel through the center of the map.
2. Calculate the cosine of this latitude value. The center parallel in CA2010.GSB is approximately 37.27 degrees. The cosine of 37.27 is 0.80.
3. Select Map in the Contents window.
4. In the Properties window, click the Scale tab.
5. Set the X scale for the map to be whatever you want. You can set either the Length value or the Map units per in. value. For this example, the X scale in map units is 1.72.
6. Uncheck the Proportional XY scaling check box.
7. Multiply the X scale Map units per in. value by the cosine of the latitude, 1.72 * 0.80 = 1.38
8. Enter this number (1.38) into the Y scale Map units per in. field. The map is drawn with the new scaling.

The new scaling looks more appropriate.

Updated October 15, 2021