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# GML

Also known as Geographic Markup Language and GML/XML. GML is a text-based, XML format that can represent vector and attribute data. This is an Open Geospatial Consortium specification for data interchange. More information is available at http://www.opengeospatial.org/standards/gml

## File listing

GML files are usually a single text file with a GML filename extension. Some may use XML as the filename extension:

    coal_dep.gml

XML schema documents often accompany GML files that have been translated from some other format (e.g. using the ogr2ogr utility).

GML uses sets of nested tags to define attributes and geometry coordinates. Example of text in a GML file:

    <gml:featureMember>
    <Coal_Deposits fid="1">
    <UNKNOWN>0.000</UNKNOWN>
    <NA>0.000</NA>
    <ID>2</ID>
    <ID2>2</ID2>
    <MARK>7</MARK>
    <COALKEY>110</COALKEY>
    <COALKEY2>110</COALKEY2>
    <ogr:geometryProperty>
    <gml:Point>
    <gml:coordinates>78.531,50.694</gml:coordinates>
    </gml:Point>
    </ogr:geometryProperty>
    </Coal_Deposits>
    </gml:featureMember>

## Data Access / Connection Method

- GML access is available in MapServer through OGR. More information on OGR GML support is available at http://www.gdal.org/ogr/drv_gml.html

- The CONNECTIONTYPE OGR parameter must be used.

- The path to the GML file is required, including file extension. There can be multiple layers in a GML file, including multiple feature types.

## OGRINFO Examples

Using ogrinfo on a single GML file:

    > ogrinfo /data/gml/coal_dep.gml
    Had to open data source read-only.
    INFO: Open of `coal_dep.gml'
    using driver `GML' successful.
    1: Coal_Deposits

Using ogrinfo to examine the structure of one layer:

    > ogrinfo -summary /data/gml/coal_dep.gml Coal_Deposits
    Had to open data source read-only.
    INFO: Open of `coal_dep.gml'
    using driver `GML' successful.

    Layer name: Coal_Deposits
    Geometry: Unknown (any)
    Feature Count: 266
    Extent: (23.293650, 37.986340) - (179.272550, 80.969670)
    Layer SRS WKT:
    (unknown)
    UNKNOWN: Real (0.0)
    NA: Real (0.0)
    ID: Integer (0.0)
    ID2: Integer (0.0)
    MARK: Integer (0.0)
    COALKEY: Integer (0.0)
    COALKEY2: Integer (0.0)
    LONG: Real (0.0)
    LAT: Real (0.0)

Map File Example:

    LAYER
    NAME coal_deposits
    TYPE POINT
    STATUS DEFAULT
    CONNECTIONTYPE OGR
    CONNECTION "gml/coal_dep.gml"
    CLASS
            STYLE
                    COLOR 0 0 0
                    SYMBOL 'circle'
                    SIZE 6
            END
    END
    END