GIS For Dummies®

Chapter 5

Understanding the GIS Data Models

In This Chapter

Finding your way around a raster representation

Exploring vector models

Entering surfaces into the computer

When you read a map, you must be able to visualize what the real world represented by the map looks like. As a GIS analyst, you need an understanding that goes beyond looks because you use this symbolic information to analyze and combine data, and more importantly, make decisions about the space that the map represents. In some cases, you lose the graphical elegance of a paper map in the computer version because the computer emphasizes computational effectiveness over good looks.

In this chapter, I help you understand how the data models that the software uses work so that you understand both the limitations and the power of a GIS.

Examining Raster Models and Structure

A checkerboard represents a unit of space divided into squares upon which the checkers rest. Likewise, raster GIS grids (the checkerboard) are broken up into grid cells (the squares) upon which geographic features (plants, animals, houses, towns, rivers, and so on) rest. On a checkerboard, the checkers are like occupants of the geographic space — you can move them around in different places. But the checkers have to stay on the dark-colored squares and move between them diagonally. In other words, the checkerboard restricts where you can place features (checkers) and where you can move them. Similarly, geographic space has limitations about what ...