Geographic Information System/Raster Model

The raster data model best represents continuous objects such as temperature or elevation. A raster can take the form of a regular set of cells, like pixels in a photograph or it can appear as cells arranged in a grid pattern, which is also referred to as a matrix.

Each cell in the raster contains a single value, and the coordinate of each cell in the raster refers to the center of the cell. Therefore, the single value stored in each cell of the raster applies to the entire cell in the raster matrix. Each cell can be defined by a cell dimension such as the cell width and height. Often, cells in a raster are square, so the cell width and cell hdight will be the same.

(Image of raster grid showing axis and coordinates)

In GIS, it is important that we know the resolution of the raster. The raster resolution is the size of each cell in the raster. Unlike how photographers represent resolution, as the number of megapixels their camera uses, in GIS, we are not as concerned about the number of cells, but of how much area on the ground each cell covers. There is a direct trade-off between resolution and file size, the cell coordinate is a center of the point cell, and the coordinate applies to the entire cell area.

It is important to reiterate that each raster cell represents a given area and the value assigned applies to the entire cell area. If there is more than one value, they can fall inside the raster cell, and then the raster cell may contain the average, central, most common, or only value covered by the cell.

Key Facts
Raster Resolution
 * The cell size is the resolution
 * There is a trade-off between resolution and raster file size
 * The cell coordinate is the center point of the cell
 * The coordinate applies to the entire cell area
 * Each raster cell represents a given area and the value assigned applies to the entire cell
 * The raster cell value represents the average, central, most common or only value covered by the cell