Spatial Thinking in Planning Practice: An Introduction to GIS

5 tor output looks more accurate, but you can increase pixel resolution to something resembling vector resolution (this, however, greatly increases the database size). In the following we try to list the advantage and disadvantag- es of vector and raster !le. VECTOR ADVANTAGES: 1. Intuitive . In our minds, we picture features discreetly rather than made up of contiguous square cells. 2. Resolution . If the locations of features are precise and accurate, you can maintain that spatial accuracy. "e features will not 'oat somewhere within a cell. 3. Topology . Although the raster data model preserves where features are located in relation to one another, they do not represent how they are related to one another. "is complex form of topology can be con- structed in most vector systems, so you can track the connections in a municipal water network between pipe and valve features and thus track the direction and 'ow of water. 4. Storage . Vector points, lines, and simple polygons use little disk space in comparison to raster systems. "is was once a major consideration when hard-disk storage was limited and expensive. VECTOR DISADVANTAGES: 1. Geometry is complex . "e geometrical algorithms needed for geoprocessing, for example polygon overlay and the calculation of distances, depending on the projection/coordinate system used, require experienced programmers. "is is not usually a problem for most GIS users since most functions are directly coded in the so$ware. 2. Slow response times. "e vector data model can be slow to process complex datasets especially on low-end computers. 3. Less innovation. Since the math is more complex, new analysis functions may not surface on vector sys- tems for a couple of years a$er they have debuted on raster system. RASTER ADVANTAGES: 1. Easy to understand . Conceptually, the raster data model is easy to understand. It arranges data into col- umns and rows. Each pixel represents a piece of territory. 2. Processing speed . Raster’s simple data structure and its uncomplicated math produce quick results. For example, to calculate a polygon’s area, the computer takes the area contained within a single cell (which remains consistent throughout the layer) and multiples it by the number of cells making up the poly- gon. Likewise, the speed of many analysis processes, like overlay and bu#ering, are faster than vector systems that must use geometric equations. 3. Data form . Remote sensing imagery is easily handled by raster-based systems because the imagery is pro- vided in a raster format. 4. Some analysis functions (surface analysis and neighborhood functions) are only feasible in raster sys- tems. In addition, many new analysis functions appear in raster systems before migrating to vector sys- tems because the math is simpler. Chapter 1: De!ning a Geographic Information System