Guide: Calculating measurements in equirectangular maps
This is a roleplay guide on how to calculate measurements, such as distances, land areas, and lat/long coordinates, from a map made as an equirectangular projection. The information contained within is primarily applicable to the Pacifica canon, but may be applied elsewhere whenever equirectangular maps are involved.
Implementation
The method employed in this guide uses Google Earth to wrap an equirectangular map onto a sphere and align it with RL latitude & longitude, from which Google Earth’s built-in tools can be used to take measurements and coordinates.
Below is a step-by-step guide to implementation, using the Pacifica canon maps as an example.
- Download the map(s) that you wish to use; this guide will use the Pacifica map and the whole-planet Pacifica map.
- Open Google Earth. It can be opened in-browser or downloaded as an application.
- Add the whole-planet Pacifica map to Google Earth as an overlay and set its transparency to 0%. It will initially render as a large rectangle covering only a portion of Earth’s surface, so this will need to be adjusted.
- Cover the Earth with the new overlay. The easiest manner of doing this is to first align the map’s upper and lower edges with the poles before wrapping the map’s left and right sides around the globe. While you are doing the left/right wrapping, ensure that the map’s prime meridian is aligned with the Google Earth GUI’s displayed prime meridian in order to allow for direct conversion of Google Earth coordinates to in-canon coordinates.
- Because the whole-planet map of Pacifica is relatively low in resolution and does not show borders, it is recommended to apply the main Pacifica map in combination with the whole-planet map. This is done by adding it as an overlay in the same manner as the previous map, with some changes: the map should be added at 50% transparency so that the whole-planet map is visible under it, and can be properly aligned by matching the two maps’ lat/long markings and continent shorelines with each other. Once this is done, set the primary map’s transparency to 100% in order to improve visibility.
- Now that your maps are added and aligned, you can take measurements using Google Earth’s ruler tool. This will allow you to find straight-line distances, curved-path distances, and land areas, as well as other information. Google Earth’s GUI will also show latitude and longitude coordinates for any location that you mouse over by default, which can be used directly if the map is aligned properly.