Geography Markup Language

Long name Geography Markup Language
Short name GML
File extension .gml

The Geography Markup Language (GML) is an XML encoding of geographic information. GML Versions 2.1.2 is supported for import by GDB. You can obtain the specifications in portable document format (PDF) from the Open Geospatial Consortium (OGC) website:

opengeospatial.org

The general model for conversion from GML to GDB is:
  1. Each GML feature type defined in an application schema becomes one GDB vector layer.
  2. For each GML feature, one GDB shape is created.
  3. With a child feature, there is a GDB field indicating its parent layer name and shape ID.
  4. Point, LineString and LinearRings geometries are supported. Other geometries defined in terms of these three are supported as GDB rings.
There are limitations to how the data can be converted.
  1. Where there are multiple schemas that each define the same element, only the first one is used.
  2. GDB supports projection information in GML document formated like "xxxxxx1234". It treats the number at the end of string as an EPSG code. Meter is the default projection setting.
  3. GDB does not support any kind of x-link:
    • Attributes are lost
    • Geometry could be incorrect

    Therefore, GDB does not support topological spatial information.

  4. Complex type-definition information is lost, but the field values within it are preserved.
  5. With XML data types, only double, float, decimal, and string types convert to GDB-field data types. Others are converted to a string type.
  6. Multiple geometries for the same feature are added as GDB rings.
  7. If there are multiple fields for the same element, only the last one is kept.
  8. boundedBy elements are ignored. Elements location and extentOf are used.
  9. GDB doesn't recognize interior or exterior rings.

© PCI Geomatics Enterprises, Inc.®, 2023. All rights reserved.