Projection Engine Data
Configuring Projection Engine Data for download to users’ devices provides them with better projection accuracy and measurements for a particular part of the world that is more unique according to the spatial reference that you tend to utilize. Additionally, the map is easier for runtime to calculate distances and ensure that items are located correctly in the map, especially when there are multiple, different spatial references involved with different layers that are placed in the map.
Projection Engine Data is only useful if you want to leave your Spatial Reference Source as WGS84 but keep your operational data in your own chosen coordinate system.
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The locations in the list available for download are provided by Esri. Not all areas of the world are available, so you may want to select the areas closest to your users’ devices.
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Be aware that Projection Engine Data is downloaded whether users are on Wi-Fi or a metered connection. The amount of data to be downloaded is provided in a running total on the left.
Recommendations
Depending upon which basemaps you use most frequently, we recommend that you consider one of the following options:
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If you want to use Esri’s online basemaps, you should set your Spatial Reference Source to WGS84 for performance reasons; i.e., the app performs better and operational data is drawn more quickly and accurately. When set to WGS84, and users are located in a different part of the world (either in or near an area in the list), then Projection Engine Data can be downloaded for that area for improved map accuracy.
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If the primary basemaps that you are using are their own cached tile services or downloaded tile packages (or vector tile packages), and use of Esri’s online basemaps doesn’t necessarily concern you, meaning you are working almost entirely with your own data and coordinate system, then you should set your Spatial Reference Source to the one of your choosing. This does not need to be set to WGS84 since not using online basemaps means performance is not hindered.
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If you absolutely must use Esri’s online basemaps and you want the Spatial Reference Source to be one of your choosing, while this is possible, it is not a recommended scenario. For example, if users are walking or driving with GPS tracking enabled, they are going to detect a significant decrease in performance.
For more information about spatial references and their importance, see Esri’s spatial and data analysis article.