W J 20: Smith et. al Introduction to GIS

Here’s an informative link to an explanation about what a raster is

Fig. 1 "A raster consists of a matrix of cells (or pixels) organized into rows and columns (or a grid) where each cell contains a value representing information, such as temperature."

Cartograms

I have never seen a cartogram before, so I looked it up to find an example.  The map below shows the US states scaled to their population size.  Therefore, Rhode Island, with a population of 1.1 million, appears twice the size of Wyoming, even though Wyoming is 60 times the acreage of Rhode Island (Fig. 2).

Fig. 2 Cartogram scaling the US states by population.

Choropleth maps use shading to represent categorized classes of a certain attribute being mapped (Fig. 3)

Fig. 3 Choropleth the amounts of water withdrawal in each state.