Mapping Hacks

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Chapter 6, Mapping on Your Desktop

#68 Convert Geospatial Data Between Different Formats

HACK

GIS gurus like to say that “raster is faster, but vector is corrector.” Vector

data is made up of points, lines, and polygons. It’s typically used to repre-

sent individual locations, such as water, rail and road networks, political

boundaries, park areas, municipal districts, military reservations, and so on.

Of course, be it raster or vector, most geospatial data comes with a bit of

metadata, which describes everything we need to know to use the data,

including the extents, resolution or scale, data type (e.g., integer or floating

point), coordinate system and datum, and more. Sometimes the metadata is

stored in the same file or files as the data itself; more often it is stored in a

separate set of files, which are sometimes referred to as world files or projec-

tion files.

Different GIS formats abound, many of them legacy or pro-

prietary formats—such as ESRI’s Ungenerate, or E00, for-

mat—which have incomplete or nonexistent free/open

source implementations. We’d suggest that the canonical

forms for open geodata are GeoTIFF for raster data and ESRI

Shapefile for vector data, with the latter remaining the stan-

dard until GML stabilizes and is popularized.

For most of our open source geodata conversion desires, we need look no

further than Frank Warmerdam’s amazing Geospatial Data Abstraction

Library, ...