Map data that is required for showing the map view is loaded from the internet map servers at the moment it is required. For example, when you zoom the map on the main screen, or when you scroll the Waypoints map, new map data is required. These can be either maps for a new resolution, maps of a new area, or a new type of map because you have changed the Map Style setting. This map data is downloaded when needed and shown on the screen.

All downloaded maps are also stored in the map cache. The map cache is a storage of maps that survives shutdown of the app itself. To avoid it growing indefinitely, it has a maximum size which can be configured in the Settings. When the cache is full, the least recently used maps are automatically and silently removed in order to make place for the newer maps.

When a new map is needed, it is first looked up in the cache. Only if the cache does not contain the map in question, is it downloaded from the map server and stored in the cache. Therefore, if all maps required for the area you are flying in are present in the cache, no internet connection is needed during flight.

It often happens that you are flying in an area where there is poor internet connectivity, or where you have high internet costs. In such cases, it is beneficiary to pre-fill the cache with the maps required for that area. The preload screen does just that.

In order to preload maps, make sure you have high speed internet connectivity, preferably through WIFI. Make sure have selected the correct map style, and disabled unneeded zoom levels in the Settings (see also below). Fill in the center coordinates and radius of the area you want to have covered. When you press "Start loading", the app will ask for a confirmation, and then start loading the maps. The progress bars will show how much of the data has been loaded already. Make sure you keep the app running while the download is in progress; it will not download data when running in the background.

When the amount of data you are about to download is larger than the cache size, you will be warned about that. Enlarge the cache size, or make sure that less data needs to be downloaded, by reducing the radius, or reducing the number of required zoomlevels.

Note that if there is data in the cache already before the download begins, and the download will fill up the cache, it will automatically and silently start removing the old data. That means that if you preload two separate areas after each other, the second download might overwrite maps downloaded for the first area. You will not be warned about that.

When the download seems to stall, and the progress bar turns red, this is most likely due to map server throttling. The map servers allow only a certain amount of data to be downloaded at the same time. When you try to download more, then they stall. Switch off the app, and try again after a couple of hours. The part of data that was already downloaded will remain in the cache and will not be downloaded again when you retry.

You will get a warning when you try to start a download that will likely lead to map server throttling.

Note that a stalled download can also mean that you have lost internet connectivity.

Each of the zoom levels supported by Flyskyhy require separate maps to be downloaded. When preloading maps, maps for all the enabled zoom levels will be downloaded. In order to reduce the amount of data that needs to be downloaded, you should therefore disable all zoom levels that are unneeded before starting the preload.

Especially the high resolution zoom levels, marked with "1250 m" and "2500 m" in the enabled map scales, require a lot of data to be downloaded. Those two levels together represent about 93% of the required data.

You can find the Enabled Map Scales setting under Maps in the Settings pane.

It is hard to give a general estimate of the amount of data that is downloaded when loading maps. The amount obviously depends on the size of the area, and which zoomlevels are enabled. But it also depends on the size of the underlying maps, how much detail the terrain has, and surprisingly even on the latitude of the location. But to give a ballpark figure for how much data is involved approximately, you can assume that an area with a radius of 50 km (31 miles) will download approximately 1 GByte if all zoom levels are enabled. Switching off the two most detailed zoom levels will reduce that to approximately 64 MByte.
A doubling of the radius to 100 km (62 miles) will quadruple the amount of data required.

When you press the "Start Loading" button, the app will do a more accurate calculation of the amount of data that is needed for that area. If that amount is more than the size of the cache that you have specified, then you will get a warning. That way, you will at least not download data that will be thrown away immediately because it will not fit in the cache.

Note that data which is already in the cache will not be downloaded again. If you need to download data for a large area, then you can use this fact to perform the download in stages. Switch off all but the least detailed zoom levels at start, and perform a preload for that. Then switch on an extra zoom level and repeat the same preload. The second preload will only download the maps needed for the more detailed zoom level. Repeat this until you get a warning for too much data. That way, you can limit the amount of data to be used, and still download for the area that you want.