The first long in each pair is the latitude and the second the longitude of a point. The first point in a segment indicates where to start drawing the line. Each subsequent point continues the line.
A break to start a new line is indicated by a pair with the first long set to -1 (minus one) instead of a latitude. In these cases the second long in the pair is ignored and drawing is restarted at the following pair.
For example, here is a tiny fragment of data to draw some parts of the London Terminal Control Area.
| Sample Line Data | ||||
|---|---|---|---|---|
| First long | Second long | Position | ||
| Hex | Decimal | Hex | Decimal | Latitude/Longitude |
| 0x0081e926 | 8513830 | 0x00a55514 | 10835220 | N51°53.83' E000°35.22' |
| 0x0081ce46 | 8506950 | 0x00a55a64 | 10836580 | N51°46.95' E000°36.58' |
| 0x0081ca2c | 8505900 | 0x00a52666 | 10823270 | N51°45.90' E000°23.27' |
| 0x0081e926 | 8513830 | 0x00a55514 | 10835220 | N51°53.83' E000°35.22' |
| 0xffffffff | -1 | 0xffffffff | -1 | Line Break |
| 0x0081b46a | 8500330 | 0x00a40b6e | 10750830 | N51°40.33' W000°49.17' |
| 0x0081c964 | 8505700 | 0x00a3f1a6 | 10744230 | N51°45.70' W000°55.77' |
| 0x0081db70 | 8510320 | 0x00a4588a | 10770570 | N51°50.32' W000°29.43' |
The first four positions define the triangular segment. The -1, -1 pair "lifts the pen" for the move to the next three points which define the two straight lines which form a fragment of another segment.