3.1. Raster and Vector

The terms raster and vector are used throughout this chapter. They both refer to specific types of data. Raster data is organized as a matrix or grid that has rows and columns; each row/column intersection is a cell or pixel. Each cell has a value, for example, an elevation. Images and digital elevation models are rasters. They are a specific number of pixels high and wide, with each pixel representing a certain size on the ground; for example, Landsat satellite images are 185 x 185 km in size. Each pixel is 30 x 30 m in size.

Vector data is represented as coordinates that define points or points that are strung together to make lines and polygons. This data often has an associated table of information, one for every feature (point, line, or polygon) in the dataset. Keeping these distinctions in mind will help you better understand the remaining parts of this chapter.