Spatial Thinking in Planning Practice: An Introduction to GIS

4 Figure 1.2. A simple vector map, using each of the vector elements: points for wells, lines for rivers, and a poly- gon for the lake. Source: Wikipedia. http://en.wikipedia.org/wiki/GIS_!le_formats RASTER DATA MODEL "e raster data model is widely used in applications ranging far beyond geographic information systems (GISs). Most likely, you are already very familiar with this data model if you have any experience with digital photographs. "e raster data model consists of rows and columns of equally sized pixels interconnected to form a planar surface. "ese pixels are used as building blocks for creating points, lines, areas, networks, and surfaces. Although pixels may be triangles, hexagons, or even octagons, square pixels represent the simplest geometric form with which to work. Accordingly, the vast majority of available raster GIS data are built on the square pixel. "e contrast between raster and vector model re'ect the ‘pixilization’ of a raster, which would be points, lines and polygons in a vector data model (Figure 1.3). "e raster data model is a part of a later chapter. Figure 1.3. Visual depiction of the di#erence between a raster (le$) and vector (right) data model. Source: GIS Commons. http://giscommons.org/introduction-concepts/ VECTOR VS. RASTER Which is better? Although GIS users have their own personal favorite data model, the question of which is “bet- ter” is an incomplete question. "ere are advantages and disadvantages to both data models, so a better ques- tion is which is better for particular applications or datasets. Some in the GIS industry use the slogan “Raster is faster, but vector is corrector.” While this is a good starting point, it conceals the details. Yes, your computer can process raster data quicker, but today computer processors are so fast the di#erence may be negligible. Yes, vec- Chapter 1: De!ning a Geographic Information System