Plotting temperatures by geographical area

It may often be more convenient to plot temperatures for a given geographical area of the globe, rather than by country. An example of this is as follows:

    tempgraph --ghcn v2.mean --start 1900 --wmo wmo.txt --kml test.kml --area "57N,8W,55N,2E"

This plots data for weather stations which are located inside a square region having top left coordinate 57 degrees north/8 degrees west and bottom right coordinate 55 degrees north/2 degrees east - an area approximately corresponding to Scotland. The resulting graph looks like this:

Also a KML file is produced which allows you to view the locations of the weather stations within the specified area using Google Earth. If any weather stations have no temperature data for the time period specified then they do not appear on the graph. An overall average graph is also produced, which merges the temperatures for the individual stations together into a mean value.