We obtained a map of the world and downloaded the GCHN list of weather stations. We plotted the weather stations on the map. The oldest stations are red and the newest are blue. We plot the older stations last, so the numerous new stations do not cover them up. Click on the figure below for a higher-resolution version, which shows the station colors more clearly.
We see early-nineteenth century stations in Europe and North America. In the twentieth century we see the stations spreading across the world, and in particular to nations near the equator. These are the stations included in the GCHN database, which are the ones used by CRU and NCDC to obtain their global surface trend. There are, however, many more stations listed as active today by the WMO. We plot these in a separate graph. In particular, we note the large number of stations listed by the WMO in Russia, but not included in the GHCN database.