Mapping Hacks

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Chapter 6, Mapping on Your Desktop

#68 Convert Geospatial Data Between Different Formats

HACK

FENAME: String (30.0)

FETYPE: String (4.0)

FEDIRS: String (2.0)

CFCC: String (3.0)

...

The -ro option in ogrinfo stands for “read-only” and is there mostly just to

spare the warning about TIGER/Line being read-only. More importantly,

the

-so option stands for “summary only”; try running ogrinfo on the

TIGER/Line

CompleteChain layer without it! The layer metadata more or less

speaks for itself. The layer consists of line strings—as opposed to polygons

or points—and the

GEOGCS["NAD83", ...] bit tells us that the coordinate sys-

tem is latitude and longitude, using the NAD 1983 datum. After the meta-

data properties, we get a list of data attributes associated with each

geometric feature in the layer. So far, so good.

You might be wondering what a geometry type of “None”

signifies. In this case, it represents data in TIGER/Line that

isn’t attributable to any particular geometric feature. OGR

can extract the values to a DBase-type .dbf file, but that’s

about it.

Now, let’s extract the CompleteChain layer—which is, in this case, all the line

segments of various kinds in San Francisco—into a more portable ESRI

Shapefile, possibly for import into another GIS application.

$ ogr2ogr -f "ESRI Shapefile" san_fran.shp TGR06075.RT1 CompleteChain

$ ls san_fran.*

san_fran.dbf san_fran.prj san_fran.shp san_fran.shx

Here, we’ve ...