Cartographica's most basic unit of information is an Feature. A feature is a geometric container for information. Usually, we represent a feature as a point, line, polygons, or imagery. Point data is the most basic and represents a location in 2d or 3d space. Line data is the next most complex and represents a series of points in a particular direction which are connected. Polygon (also sometimes called Area) data is the most complex data and represents a series of points which surround an area, optionally containing "holes" that cut areas out.
All feature types are available in single and Multi-part features. Multi-part features provide a way to consider a group of geographical elements as a single unit. This can be helpful for representing many types of data. For example, multi-point features (multi-part points) can represent grouped locations for a particular event type or time period; multi-line features can deal with maintaining a single record for a road that is discontinuous; and multi-area features can provide a single feature to represent an archipelago. These are just examples, and you can use them in unique ways to represent your data.