Supposing we want to filter our data by a given region, it's possible to assume that this region is represented by a polygon.

For example, the following image represents the world counties' borders, it was rendered from a Shapefile where each feature is a country and it's geometry is a polygon.

Differently from the geocaching point, whose geometries are only a pair of coordinates, a polygon is a sequence of at least three-point coordinates beginning and ending at the same point.

By now, you can assume that we won't be able to store the polygon's coordinates with the same structure that we had with the geocaching point. We will need to store the whole OGR geometry or store something that can be transformed from or to it.

How these polygons are represented is an important subject, because mastering it allows you to manipulate them any way you need to do any kind of work. It also allows you to build polygons from point coordinates (from a GPS for example) or form shapes such...