Choropleth maps of London Boroughs

Please find below a choropleth map the population densities in the various London boroughs. After wasting too much time colouring in maps using MS Paint, I thought there must be an easier way, so I had a go at drawing a stylised map of London borough using SVG.

Most of free svg maps online used paths to trace each borough, I wanted polygons so I had to draw it from scratch.
The population densities are calculated from wikipedia figures from the 2011 census.

I've used html titles for the tooltips.

The map renders fine in Chrome 27.0.1453.116, not at all in internet explorer 9.0.8112, haven't tried it in Firefox.

I'm not sure about the colour scheme, greyscale looks okay for the time being. Any suggestions and critique would be gratefully received.