Web Mapping Illustrated

Name

National Transfer Format Files (NTF)

Synopsis

NTF files are mostly used by the U.K. Ordnance Survey (OS). For more on the Ordnance Survey, see their web site at http://www.ordnancesurvey.co.uk.

File listing

NTF files have an NTF extension.

Data access/connection method

• NTF access requires OGR.

• The path to the NTF file is required in the CONNECTION string. It may be relative to the SHAPEPATH setting in the map file or the full path.

• The CONNECTION must also include a layer number (as per the layer number from ogrinfo, but minus one).

ogrinfo examples

Here's an example that uses ogrinfo on an NTF file to retrieve layer numbers:

    > ogrinfo llcontours.ntf
    ERROR 4: NTF Driver doesn't support update.
    Had to open data source read-only.
    INFO: Open of 'llcontours.ntf'
    using driver 'UK .NTF' successful.
    1: LANDLINE_POINT (Point)
    2: LANDLINE_LINE (Line String)
    3: LANDLINE_NAME (Point)
    4: FEATURE_CLASSES (None)

For the LANDLINE_LINE layer, the ogrinfo layer number is 2; however, when referring to this layer in a map file connection, the layer number is 1.

Here's an example that uses ogrinfo to examine the structure of an NTF layer:

    > ogrinfo llcontours.ntf LANDLINE_LINE ERROR 4: NTF Driver doesn't support update. Had to open data source read-only. INFO: Open of 'llcontours.ntf' using driver 'UK .NTF' successful.   Layer name: LANDLINE_LINE Geometry: Line String Feature Count: 491 Extent: (279000.000000, 187000.000000) - (280000.000000, 188000.000000) Layer SRS WKT: PROJCS["OSGB 1936 / British National ...