Better map experience

At the moment, the nodes map displays a map, and it knows the lat/lng coordinates of the min and max corners of the map, allowing it to interpolate the position of any node and display a map pin.

We’re deliberately not using a mapping service for this, even open street maps, so that it works simply and offline.

However, it’s a shame that the map doesn’t display nodes that fall outside the map, or nodes that don’t have coordinates yet.

Completed when

• If there are nodes outside the map border, the map gains a margin round the edge to display them
• Nodes outside the map bounds display in the margin area, making it clear they aren’t on the map.
• An arrow to each of these nodes indicates the distance off the map
• A separate section below the map shows a simple list of nodes with no coordinates