How are the thumbnails automatically generated (and why do some maps not have them?)

[BrettGreenfield__DNR_]

I have a number of maps created and saved on my ArcGIS Online account.  When I save the map - in most cases - the thumbnail is automatically generated based on the extent of the features; it shows the basemap and the layers added to the map.

For some of my maps, though, there is no thumbnail at all.  I also tried changing the basemap on one service, but I didn't see the change reflected in the thumbnail.  The only idea I've come up with so far is that all of the offending maps are using large layers (>2mb in size); but, not all of the maps with large layers are experiencing this problem, so I'm not sure if that's related.

I know I can add a thumbnail image myself, but taking a screen grab of the map and shrinking it to fit the thumbnail requirements is a cumbersome process that I'd like to avoid if possible.

[MikeMinami]

The thumbnail should show what's in the layer. However, because the scale of the thumbnail is different from the map in the viewer, some layers might be out of scale range. Also, ArcGIS Online can't display layers on an internal network as part of the thumbnail.

The thumbnail gets updated every time you save the map from the viewer.

If you're not seeing this, there may be some bugs. Perhaps you can share a link to the map(s) that have thumbnail issues.

Thanks,

Mike

[PaulLohr]

Having the same issue.

[BrettGreenfield__DNR_]

Thanks for the response.  Here's a link to a map having this issue: http://maryland.maps.arcgis.com/home/item.html?id=748787ded9864b3fba6d32843a1ebb72.  The map is zoomed to the state of Maryland, which is in the scale range of the layer, and it was added directly to the map.  The only common theme I can see throughout these maps is the file size of the layers in them - they're all pretty darn big.  However, other maps with large, complex datasets seem to be fine, so I'm not sure that has any relevance.