Land-Line NTF file (NTF)

Land-Line data is an enhanced vector data set, where features are represented as points and lines that are digitised and specifically coded to show differing features. It is not a structured data set and, as such, does not contain defined polygons.

Structure of features

The structure of each different feature is as follows:

1. Points - these consist of:
   • a Point Record [POINTREC] 15
   • a Geometry Record [GEOMETRY1] 21
   • and can have an associated Attribute Record [ATTREC] 14, which contains a measurement for variable sized symbols
2. Lines - these consist of:
   • a Line Record [LINEREC] 23
   • and a Geometry Record [GEOMETRY1] 21
   • and maybe one or more Continuation Records[CONTREC] 00 to extend the Geometry Record
3. Text - this consists of:
   • a Name Record [NAMEREC] 11
   • a Name Position Record [NAMPOSTN] 12
   • and a Geometry Record [GEOMETRY1] 21

Coordinate referencing system

Abbreviated National Grid coordinates are supplied and are given in centimetres. The coordinates have a field width of 6, not the NTF default width of 10. Full National Grid coordinates are calculated by using the {XY_MULT}, {X_ORIG} and {Y_ORIG} values in the Section Header Record [SECHREC] 07, and the conversion formulae below:

X = ({XY_MULT} x {X_COORD}) + {X_ORIG}
Y = ({XY_MULT} x {Y_COORD}) + {Y_ORIG}

where {X_ORIG} and {Y_ORIG} are additive constants, always added to {X_COORD} and {Y_COORD} respectively, whilst {XY_MULT} is a multiplication factor applied to coordinates before the addition of {X_ORIG} and {Y_ORIG}. Negative coordinate values may be carried in {X_COORD}, {Y_COORD}. In each case, the minus sign appears as the first character of the field.

See UK National Transfer Format (NTF) for information on georeferencing.