The purpose of the Offline Areas is to pre-cache raster base layers to the mobile device so it would be available offline. The main use case for this feature is following: let us say a user going in the field to collect data. There will be no data connection there. The user can outline the area and select a base layer(s) that need to be available while offline. Then the user needs to download offline areas to the mobile device. Here are few simple steps to achieve that.
1. Click on the "Offline Base Layers" button on left hand side of the page.
2. Click on the "Add Area" button on the right hand side.
3. Type the name of the Offline Area.
4. Create a polygon of the offline area by clicking a button on the left hand side of the view and hit Save.
5. The offline area can be shared between the users of this project. To give other users access to this offline area click on the "Edit Users" button on the right hand side and select users that shall access to this offline area. Users need to accept the invitation to this project to be able to use this offline area.
6. To define which base layer shall be used as a part of this offline area click "select" in the list of users under the map.
7. Select a base layer to be available while offline. The "Disk Size" value is an estimation of how much storage this offline area will take on a mobile device. This is not an exact value, but just an estimation.The actual size is depends on the imagery compression. The shown value is a "worst case scenario", usually it takes less. To control the size change the Max Zoom Level.
8. The Offline Area is ready to be used on the mobile device. To download the Offline Area to the mobile device, select the project. After project is synced to the device the Offline Area button will appear in the top bar.
9. Tap "Download" to start the Offline Area download. During the download, the progress will be shown in the list.
10. While the Offline Area download is in progress, the Status view will show more detailed information.
11. After the download is finished the Offline Area will be available even when there is no data connection. To view the Offline Area select the corresponding Baselayer.