Introducing Geographic Information Systems with ArcGIS: A Workbook Approach to Learning GIS, 3rd Edition

Rasters and Features

As you work through this chapter, you will get a feel for the differences between vector and raster representation. Here I simply want to let you know that you can convert from one data model to the other—albeit with loss of information each time.

Let’s consider operations in which the inputs are feature classes and the outputs are rasters: the simple conversion from feature data set to raster data set. To do these conversions, you can use the tools in ArcToolbox.

If you convert a point feature class to a raster, each cell that has a point within its boundary takes on the value of that point. If more than one point exists within the boundaries of a given cell, the software randomly picks one of them to represent in the cell. In terms of attributes, the VAT value is taken from the feature attribute table field that is specified by the user. If that field is an integer number, it becomes the VALUE attribute in the VAT. If the user-specified field is a floating-point number that number becomes Value in the VAT if there aren’t too many of them. If the user-specified field contains text, then an additional field is added to the VAT, containing the field name, and the Value field becomes a randomly assigned integer.

If you convert a line feature class to a raster, each cell that contains any part of any line takes on the value of the line, according to the field specified by the user. The rules for what goes in the VAT are the same as for points, discussed previously. ...