So far in our GIS work, although it pains me to say it, we have had all of the disadvantages and none of the advantages of the fact that the world (and everything in it) resides in four dimensions. The disadvantages have come about partly because (1) the Earth is approximately spherical—requiring all that projection complication in moving from three spatial dimensions to zero, one, or two dimensions—(2) three-dimensional stuff is just harder to deal with, so we have contented ourselves with “flatland” in which nothing is quite right, and (3) it’s hard enough just to get a dataset right at a given moment or period in time—never mind historical or anticipatory data sets.
But now we take on, separately, the third spatial dimension and the time dimension.
I present the Overview and the Step-by-Step sections together for each topic. When we say 3-D GIS, we usually mean three spatial dimensions. The title of the next section is meant to convey that idea. However, in the section after that, which is “3-D: 2-D (Spatial) Plus 1-D (Temporal),” we will take up looking at what happens to two-dimensional data over time.