6.2.1
A level 1 LSG contains the most basic representation of spatial information. Two extremity points are recorded at opposite ends of the Street.
6.2.2
The start and end points of a Street are the two extremity points of the centreline network of ESUs for that Street.
6.2.3
Street Data within level 2 LSGs is made up of ESUs and must be built upon a level 1 LSG. For further details, see Section 11.
6.2.4
Level 3 Street Data also contains ESU Records. This data builds upon a level 2 LSG by defining the complete geographical shape of the Street. This is done by recording a string of coordinated points that help to define the entire shape of the ESUs.
6.2.5
Therefore, level 3 Street Data defines the true shape of the Street. Streets defined to level 3 contain at least one ESU Record (from level 2) with intermediate points as necessary. The start and end points of each ESU are recorded in the type 13 Record, and all the intermediate points in type 14 Records.
6.2.6
Level 1 and level 2 gazetteer data can be derived from level 3 gazetteer data in the following ways:
- Level 1 – by using Street extremity points.
- Level 2 – by using ESU extremity points.