ggplot2heat mapr
I'm using R with ggplot2 to generate maps from shapefiles and from data in SQL Server. I'm trying to get to a stage where I can automate a large chunk of the mapping I do. So far this is working well and I'm able to generate some fairly nice looking maps (just need to work on labelling).
I'm wondering if it's possible to create a geographical heatmap from a list of point co-ordinates (which are irregularly spaced)? Similar to using geom_density2d, but raster.
Some options:
Use the OpenLayers Plugin. This plugin allows you to use Google, Bing or OSM's tiles as background image.
Create a custom vector style similar to Google or OSM. Underdark made a series of post on how to do this with OSM data using the New Symbology Rule based rendering. She even provided the qml in github.
There are some great resources on exactly this very interesting subject, including:
From Revolutions:
From Stack Overflow.se:
Developing Geographic Thematic Maps with R
There are excellent examples of choropleth maps and their associated R code, including my favorite (i.e. attached map) using ggplot2. It should be relatively straight forward to insert your own data set into one of the script examples.
R Code for this map available from This is the Green Room
Best Answer
RTFM. Turns out that stat_density2d can do all I was asking and more.
Edit:
Still one outstanding issue with this which is that using stat_density2d with geom=tile can display some odd behaviour when trying to set the scale of the map.
In my example I am plotting a shapefile of all England & Wales, however I'm interested in the greater London area. If I allow ggplot to simply default and display the entire shapefile then the heatmapping generated by stat_density2d isn't very useful for me.
To address this I need to set the xlim and ylim to effectively zoom in. I can do this in one of two ways:
The former causes the heatmapping to scale correctly (ie size of the tiles reduce to give a meaningful indication of density in a smaller area) but the shapefile data gets truncated to the plot leading to some very odd looking polygons.
The latter causes the heatmapping to remain at the scale of the whole country (ie the tiles are massive and so not useful for showing activity density) but the polygons display correctly.
I've set this as a separate question: Using stat_density2d with coord_map in ggplot2