Vector features are represented as points, lines, and areas or polygons. A point is a single location If you take a series of points and connect them to each other, you form a line. A polygon is the interior space created by two end points of a line when they close in on one another. Another way to depict a landscape is to represent it in raster format. Each pixel gets an attribute value.
Cells can be of any size.
Better for analysis of continuous data. Lends itself well to the analysis of satellite imagery. The two types complement each other, and better GIS packages can use either representation. Some are already available. You'll see some examples on Wednesday.