GeoJSON mouse over support with shapefile shapes

[peterhambly]

GeoJSON hover support with shapefile shapes. This will allow the hover mode to display data from the area geoJSON below the shapefile shapes.

I experimented with mouse click through but was unable to get to work without adverse performance implications:

• TopoJSON grid layer blocks mouse clicks unless it is the in view pane;
• Using the mouse position to find the nearest TopoJSON grid layer does work, but you only get one mouse event per layer boundary cross. We would need to modify the map shape pane to transmit more events (this may not be possible), this has performance implications as you will need to work out which GeoJSON shape is nearest the click. With tens of thousands of shapes this will be slow, requiring more complexity - e..g use 1km grids to reduce the search.

[peterhambly]

I have removed this from the making the RIF Usable by SAHSU project because of the the difficulties, and the potential to be time consuming.