In Chapter One, we examined the definition of GIS - geographic information systems and GIScience, where we started to get an idea of how spatial (where data occurs) and non-spatial (information about that location or mapped object) data are combined to explore the distribution of data and solve spatial problems. In Chapter Two, we diverted a little bit to understand the ideas behind geodesy (the science of measuring and monitoring the Earth), geographic coordinate systems (a global "address" system for labeling and locating places on the Earth's surface), and projected coordinate systems (flat maps which allow us to measure in linear units vs angular units, but come at the cost of distortion). These concepts both start to come together in this chapter where we look at types of spatial data: vector data, raster data, and data tables, because GIS software is useless without data. Like an oven without a giant dish of macaroni and cheese, the software is just a tool waiting for input to produce something gooey and delicious - like a map of all the best mac n' cheese restaurants in the city.
Within the GIS model, this chapter will deal with the representation portion, looking at how it is we represent the real world (reality) in scaled down formats capable of being downloaded whenever we wish. While we will examine several formats of data throughout the semester, all GIS data can be broken into three main categories: vector, raster, and data tables. All three types are important and necessary to solve problems using GIS, so each type will get equal emphasis.
Since GIS combines the spatial and the non-spatial, the data, too, must combine the spatial and non-spatial. In regards to our learning, this means the three major data types are not independent, but in fact, completely intertwined. When you open a spatial file, you will find it consists of several smaller files, one of which is a table full of measurements and written data that can be attributed to a specific place in the world. Map files (vectors) are often created by looking at aerial images (rasters), which then serve as the backdrop to the completed map. Additional non-spatial data is often stored in data tables, which are then joined (connected to) vector files. Raster images pair with data tables to solve spatial problems.
In this chapter, we will look at what are vector files, raster files, and data tables, how we use them in GIS, how to recognize the difference between them, go over a few special case vector and raster data types and how they interact with other data, and finish up with an introductory overview of attribute tables and how we use the in GIS. Looking ahead to Chapter Four and Five, we will look at the most used GIS software suite, ArcGIS, and a specific (and highly utilized) type of data table, an attribute table. For now, however, we will spend some time looking at the definitions and some examples of spatial data.