Webmaps - Data Models

There are two main computer models used in GIS to represent geographic features; they are known as spatial data models. In the first, the vector data model, each feature is defined spatially with discrete Easting and Northing co-ordinate pairs. In the second, the raster data model, the data is displayed as an image laid out in a grid structure where each cell, or pixel, is referenced by a particular row and column value. In a vector data model, locations are recorded as Easting and Northing co-ordinates. Points are recorded as a single co-ordinate pair, lines are recorded as a series of ordered co-ordinate pairs and areas (polygons) are recorded as a series of ordered co ordinate pairs defining line segments that enclose an area. This method means that you can look at the map feature at any scale and it will always be clear. The raster data model is a rectangular grid of cells (pixels) each with a value. Using the raster data model, the earth is treated as one continuous surface and da

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• Catherine Hoang