How to plot quadrat counts on top of a map in ggplot2 in a heatmap-like style

ggplot2, r

Solution

To add a heatmap in ggplot, you can use `geom_tile`, or its default stat, `stat_bin2d`:

library(mapproj)
base.plot +
  stat_bin2d(data=points, aes(x=lon, y=lat), bins=100) +
  coord_map()

I also suggest you use `coord_map` rather than `coord_equal`, after installing the `mapproj` package to enable different map projections.

Problem

I am trying to take a shapefile and points that are contained within it and end up with a plot of the shapefile, the points, and then eventually a quadrat analysis overlayed on top with some amount of alpha transparency. I tried and came up with this example that should serve: ``` library(ggplot2) library(maps) library(maptools) library(spatstat) library(plyr) # generate polygons usa <- map('usa', plot=F) IDs <- sapply(strsplit(usa$names, ':'), function(x) x[1]) crs <- CRS('+proj=longlat +ellps=WGS84') usa.sp <-map2SpatialPolygons(usa, IDs=usa$names, proj4string=crs) usa.pts <- fortify(usa.sp, region="id") base.plot <- ggplot(usa.pts, aes(x=long, y=lat)) + geom_path(aes(group=id)) + coord_equal() # generate point process lon <- runif(5000, min(usa.pts$long, na.rm=TRUE), max(usa.pts$long, na.rm=TRUE)) lat <- rnorm(5000, mean(usa.pts$lat, na.rm=TRUE), sd=sd(usa.pts$lat, na.rm=TRUE)/2) points <- data.frame(lon, lat) points.sp <- SpatialPoints(points, proj4string=crs) points <- points[which(!is.na(over(points.sp, usa.sp))),] # the first plot base.plot + geom_point(data=points, aes(x=lon, y=lat), color="red", alpha=I(0.5)) ``` So then what my shapefile and data would roughly look like are: The next steps I'd like to take are to perform quadrat analysis of various cell sizes and plot the results over the plot with points. Assuming I successfully get a quadratcount object (wrangling the data right now into right format), how would I go about plotting it as a heatmap-like overlay?

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