Zooming in Topo Maps in Android

Often, I get questions from people who zoom in on a map and only see a blank grid. I'll show an example that will show how this may not be a bug.

Often the question is something like this: "Sometimes I zoom in on downloaded maps and all I see is a blank grid. What's wrong?" Often nothing. 

There is a key rule to keep in mind when you define a rectangle for download:

The download will download all tiles that *overlap* the defined rectangle, for all zoom levels.

In the following screen, I've just completed a small download. Here it is at zoom level 15, the highest detail I specified when downloading.

Detailed Topo map downloaded for offline use on Android   
This map adequately covers the rectangle I specified, plus more, so I should be extremely satisfied, right?

Now I'll try zooming out three levels to level 12. At this zoom level, the rectangle I specified overlaps exactly one (1) tile which covers a wide region. 

Zooming out on a topo map on Android
 

Again, this more than adequately covers the region I specified, so I should still be satisfied. Now the interesting stuff happens if I pan around this zoom level and then zoom in. If I zoom in on the green circle above, I should expect to see some more detailed map data.

However, if I zoom in on one of the red circles above, something happens which I may not expect. The map "disappears" and all I see is a blank grid. I could be disappointed, or think this is a bug, but why? After all, I got the region I asked for.

User Actions to help 
So if this isn't a bug, then what can a user do about it? Here are some suggestions:

  • Download a larger region. You could mark a rectangle that completely surrounds the one tile at zoom 12, and then you could expect to zoom in fully at those red circles.   
  • Turn off "Offline Maps Only" in the Map Source menu to go back into preview mode. Then you can at least preview the areas with red circles, and any tiles downloaded during preview will be saved. 

Where the App could help. 
The use of tiling in maps is here to stay. Nonetheless, there are some good suggestions users have made:

  • Show a coverage viewer that will allow you to see what your map currently covers. Presumably this will show a grid where darker squares indicate higher resolution. 
  • Show a grid and allow you to tap and choose tile squares instead of defining a rectangle. This will give you more predictable results, although it won't completely eliminate "zoom-in disappointment."    

Look for some of these ideas in surveys and future updates. 
 

4 thoughts on “Zooming in Topo Maps in Android

  1. UK Ordinance Survey and New Zealand topo map do not exist in the same physical location. You can't just swap map layers. IF the screen is centered on UK, you won't see anything with New Zealand maps. 

    You need to recenter the screen with place find or waypoints. 

  2. Thanks for your reply. I understand what you mean by that now. However I still have no map data. When centered on New Zealand with the New Zealand topo on there is no map data. When centred on the UK with OS turned on Ican not zoom in to any areas I have not saved and can not save any other areas. I am at home with wi fi and the download tiles only option is not checked. Have you any idea what I might be doing wrong?
    Thanks,
    Tom.

  3. To be on he safe side, check to see how much room you have on your storage card. 

    Are the blank areas white? or are they with a grid? Or are they circles with Xs? 

  4. I sorted it out last night. That was exactly what it was no space on the SD card, as soon as I changed that it was up and running fine.
    Thanks for the support.
    Tom.

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