Creating Offline Cache Regions
One key feature of GIS Kit and Pro is the ability to download maps for offline use. This is accomplished in three steps:
- Specify Map Type (i.e. Open Street)
- Specify Region Type (Rectangular, circular, or free draw)
- Define Resolution
The result is stored as a "cache region" and can be emptied and reloaded as necessary. As of version 2.2 they can also be shared with other GIS Pro users.
Specify Map Type
This step is simply to indicate what base map (e.g. server or map type) to download the images from. The list of options comes from the the map types you have set up that have "offline mode" turned on.
Specify Region Type
Rectangular and circular regions are what you would expect. Free draw is more flexible and powerful as it allows you to indicate the region by sketching aribitrary shape(s).
You must carefully decide how high of resolution you select. Map imagery is divided into 256x256 pixel squares, each at a specific zoom level and coordinate. The higher the zoom level, the more detail is displayed. Of course, this requires more storage and bandwidth. In fact, each increasing zoom level requires four times as much data as the previous. Also, the tile server must support that high of a zoom level.
GIS Pro provides three "Quick Options" for convenience and simplicity. These are simply preselected zoom levels and full control can be assumed by the user by selecting and deselecting the actual level numbers in the "Selected Levels" box.
A great write-up of how the tile system works as well as what the zoom levels mean can be found on Microsoft's site here
Managing Cache Regions
Cache regions can be deleted by swiping on the cell representation. If they have not started downloading or have not completed the cell will also include a pause or resume button. When the app is put into the background it will pause downloading until the app returns to the foreground.
Region Details Screen
When a cache region's cell is selected the region's details will be presented in the region details screen. Here the name can be edited, the tiles can be erased, downloading can be started and the region can be shared with others.
In order to free up device storage tiles can be temporarily erased by tapping the "Erase" button. The tiles for this region can then be downloaded again by selecting the "Download Button"
- Downloading pauses while app is in background
- Downloading resumes upon app reactivation
- Downloading pauses upon network failures
- "Stuck" or "frozen" regions probably have too high of resolution specified (see Define Resolution)