Cutting up a shapefile into smaller parts
With ogr2ogr
, you can specify a bounding box that you'd like to clip by with -clipsrc x_min y_min x_max y_max
, so for example, to only get the northern hemisphere of a global dataset you could do:
ogr2ogr -f "ESRI Shapefile" borders_north.shp borders.shp -clipsrc -180 0 180 90
See the ogr2ogr documentation for further options, including clipping to another geometry.
You can install and use qgis to load the file you downloaded; use the mouse or query the data for the features that you would like to select; and export the selected features to a new shapefile.
QGIS is a cross-platform (Linux, Windows, Mac) open source application with many common GIS features and functions.
A link containing tutorials that illustrates these steps in qgis is available here http://qgis.spatialthoughts.com/