For my research on Avian Influenza in waterbirds, I recently needed data on lakes and marsh-areas in Europe. I ended up compiling a spatial dataset from a number of different sources, including the EU Corine Land Cover database (CLC2000v13), the lake depth dataset compiled by Ekaterina Kourzeneva for the FLake model and data from the Finnish national lake register. In order for this to be usable I had to relate the lakes and marshes in the different datasets to each other. In other words, I needed to find out which coordinates or polygons in the different datasets represented the same lakes, and I needed to know which marsh areas were close to which lakes.

After searching around a bit and considering several options, I decided (for several reasons) not to use a full-blown …

Shapefiles are a format developed by ESRI (the makers of ArcGIS) to store and share geospatial data. Many interesting datasets are freely available in shapefile format. Shapefiles can be viewed with a number of freely available applications, such as ArcGIS Explorer (which requires the .NET framework or Silverlight) or ArcReader (which is multi-platform but closed-source). Open-source GIS packages such as Quantum GIS and GRASS can also view and edit shapefiles, and recent versions can be installed from the UbuntuGis PPA.

However GIS applications can be tricky to use without training. Moreover, sometimes you may want to use shapefile-data for some other purpose, outside of traditional GIS applications. Here are a few useful tricks you can do with shapefiles, and ways to get data out of a shapefile and into another application.

Reprojecting a …