It is important to understand there are two kinds of maps: Some of the maps are fully downloaded in full the first time you select them. These are typically sheet maps, where there is a separate map file corresponding to each paper map. These include marine charts, aviation charts, and some 4WD maps. For these maps, the best approach is to select a Package from the digital map store listing when you download the map. This will ensure you have all the available maps in the area of the package.
The other kind of map is used for large seamless topo maps. As you scroll or zoom around the map, the app downloads just the data it needs to display, but this requires an active internet connection. These maps are not normally downloaded in full, but we provide tools to help you select the areas you need to download, and to review what areas have been downloaded to the device.
First some general tips: Make sure the device is plugged into power. Obviously running a battery flat mid download would terminate the download but many devices go to sleep at some point and that amounts to the same thing. In most devices, being plugged in, prevents it going to sleep.
Also, using another app or taking a call or text, while downloading a map puts the Memory-Map app into the background, which can have the same effect. But most devices allow apps to run in the background ONLY IF they are plugged into a power source. Generally it is best to leave the app undisturbed in the foreground if possible.
For specific details, see Here for iPhone/iPad, Here for Mac and Here for Android.
For PC, see the Help menu.
On the PC, you do not need to have the map you want to download on screen.
What you do need is the area you want to download framed either on screen or within an enclosed route.
Framed on Screen - Best to select a small scale map or basemap on screen, zoom and pan so that it covers the desired territory. Then click on the DMS button and call off the map you want from the DMS map list and let it download the chunks that you don't have. It won't duplicate the download, it just continues filling in content.
Enclosed Route - Another way is to draw a route around the area that you want to download, enclosing the route so the last waypoint is placed on the first. Again it doesn't have to be on the map you want, its all about the area. Then right click on the route and select select Digital Map Store. This will show you a list of maps only within the enclosed route. Selecting a map from the list will download all or part of the map framed by the route.