Web Mapping Illustrated

Chapter 7. Converting Map Data

Chapter 2 outlined the various tasks of digital mapping; one of those tasks involved converting data between different formats. In a perfect world there might only be one or two formats, but in reality there are dozens of different ways to store spatial information. Add to that both raster and vector data formats, and you've got quite an array of options. Like Chapter 6, this chapter by itself won't likely create beautiful maps, but the steps presented here are even more important because they are a key part of the path to producing useful maps.

The examples in this chapter use the GDAL/OGR utilities that are introduced in Chapter 6. They are part of the FWTools package.

Converting Map Data

Different data formats have sprung up because of the need for various capabilities and the desire for proprietary software control. Creating a better data format may be necessary to handle more complex information or improve performance, but having various data formats just because each vendor creates one for its own product is hardly productive. Fortunately, there are some excellent tools available for both raster and vector data conversion and for coordinate reprojection. By their natures, raster and vector data need to be handled differently, though the general concept is similar: take data in one format, and convert it to another format.

Data conversion can be necessary for a number of reasons:

• The source data may be in a format you aren't familiar with.

• Your mapping ...