SpatialPolygonDataFrame plotting using ggplot

Question

I have a shape file for the greater London area. I use the `readShapePoly` function from the `maptools` package to load it in R as a `SpatialPolygonDataFrame` . I want to the plot those polygons .. Which I have already done by using the basic of `plot` function in R. The output looks as shown in this image: Now, I am trying to plot the same shape file using `ggplot2` but it doesn't work for me. I am getting some weird lines in the graph as shown below: The code I used was : ``` london.wards <- readShapePoly("~/TD/london_wards2013/london_wards2013.shp" , proj4string=CRS(projString)) wards.count <- nrow(london.wards@data) # assign id for each lsoa london.wards@data$id <- 1:wards.count wards.fort <- fortify(london.wards, region='id') ggplot(wards.fort, aes(long, lat)) + geom_polygon(colour='black', fill='white') ``` where projString is the projection string describing the projection used for the input shape file.

Accepted Answer

You need to add an additional aesthetic, `group`. Assuming the polygon id is called `ID`, the synatx will look like:

```
ggplot(wards.fort, aes(x = long, y = lat, group = ID)) + 
   geom_polygon(colour='black', fill='white')
```

SpatialPolygonDataFrame plotting using ggplot

Solution

Problem