Table of Contents for

Web Mapping Illustrated

Interrogates a vector dataset and gives information about the features. This can be done with any format supported by OGR. The following code shows ogrinfo being used to show information about a shapefile:

                        # ogrinfo -summary placept.shp placept
    Had to open data source read-only.
    INFO: Open of `placept.shp'
    using driver `ESRI Shapefile' successful.

    Layer name: placept
    Geometry: Point
    Feature Count: 497
    Extent: (-140.873489, 42.053455) - (-52.808067, 82.431976)
    Layer SRS WKT:
    (unknown)
    AREA: Real (12.3)
    PERIMETER: Real (12.3)
    PACEL_: Integer (10.0)
    PACEL_ID: Integer (10.0)
    UNIQUE_KEY: String (5.0)
    NAME: String (50.0)
    NAME_E: String (50.0)
    NAME_F: String (50.0)
    UNIQUE_KEY: String (5.0)
    UNIQUE_KEY: String (5.0)
    REG_CODE: Integer (2.0)
    NTS50: String (7.0)
    POP91: Integer (7.0)
    SGC_CODE: Integer (7.0)
    CAPITAL: Integer (3.0)
    POP_RANGE: Integer (3.0)

This example shows many vital pieces of information including geographic extent of features, a list of the attributes, their types, and how many features are in the file. Additional parameters can be added that help access desired information more specifically.

Running it in different modes (the example shows summary mode) will reveal more or less detail. A complete listing of all the values and geographic locations of the features is possible if you remove the -summary option. You can also specify criteria using standard database query statements (SQL), as shown in the following code. This is a very powerful feature that provides access to spatial data using a common database querying language. Even file-based OGR data sources can be queried using SQL statements. This function isn’t limited to database data sources. For more information on OGR’s SQL query capabilities, see http://www.gdal.org/ogr/ogr_sql.html.

    # ogrinfo placept.shp -sql "select NAME, NTS50, LAT, LONG, POP91 from placept
    where NAME = 'Williams Lake'"

    OGRFeature(placept):389
      NAME (String) = Williams Lake
      NTS50 (String) = 093B01
      POP91 (Integer) = 10395
      POINT (-122.16555023 52.16541672)

Takes an input OGR-supported dataset, and converts it to another format. It can also be used to reproject the data while converting into the output format. Additional actions such as filtering remove certain features and retain only desired attributes. The following code shows a simple conversion of a shapefile into GML format.

    # ogr2ogr -f "GML" places.gml placept.shp

This code takes an ESRI shapefile and easily converts it to GML format or from/into any of the other formats that OGR supports writing to. The power of these capabilities is surpassed by few commercially available packages, most notably SAFE Software’s Feature Manipulation Engine (FME).