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.
To determine the adjusted scaling factors, follow these steps:
- Determine the latitude for the parallel through the center of the map.
- 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.
- Select Map in the Contents window.
- In the Properties window, click the Scale tab.
- 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.
- Uncheck the Proportional XY scaling check box.
- Multiply the X scale Map units per in. value by the cosine of the latitude, 1.72 * 0.80 = 1.38
- 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
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