The graphical representation of spatial and attribute data in GIS software takes the form of either raster or vector graphics. The differences between raster and vector graphics, as detailed below, effect the level of detail, visual appeal, speed of manipulating graphics and data storage space required.
Aerial photographs and satellite images are generally in a raster format and are used in GIS to view a detailed map at a given extent or for the purpose of digitizing. Raster graphics are predominantly used to display spatial data and use a grid-type architecture in terms of storing spatial and graphic value data. Vector graphics are commonly used to represent features like roads, rivers, housing, and the like using points, lines and polygons. Based on scalable vector graphics, vector graphics provide a linear and detailed approach to manipulating attribute data. Raster and Vector graphics are frequently used together.
The key difference between Raster and Vector graphics is how they are structured. Raster graphics use pixels (“dots”) whereby a graphic is made up of a large number of pixels, each pixel having a location & colour value in a grid-like format. A vector graphic is rendered by a mathematical manipulation referenced by co-ordinates. Given the different structure of these graphic types, the following differences arise as a result:
1. Storage Space: Raster graphics require more storage space than vector graphics, as they store a location & colour value per pixel.
2. Detail: Raster images are more detailed within a given extent (“zoom”), however raster images become pixelated if too tight a zoom is applied. Vector images are less detailed, but maintain their original aesthetics regardless of extent or zoom.
3. Responsiveness: performance & responsiveness when manipulating vector image is faster than raster images, as the data structured used to render vectors is mathematically based whereas rasters requires the retrieval of individual pixel values and a manipulation of each pixel.