PAI Toolbox: Am I affected

Which Land Line^® data is affected?

The Land-Line map tiles that are affected by the Positional accuracy improvement (PAI) programme are all those that contain data surveyed at 1:2500 scale accuracy. This covers all maps with a 1 km by 1 km format reference that, pre PAI, contain the letter B in the CONT_IND (content indicator) field, for example, SU3311. Some maps with a 500 m by 500 m format reference contain 1:2500 scale accuracy data only (pre PAI CONT_IND is B), for example, SU3313SW, or contain a mixture of both 1:1250 and 1:2500 scale accuracy, for example, SU3313SE (pre PAI CONT_IND is AB). These are all included in the PAI programme. Map tiles that only contain data surveyed at 1:1250 scale accuracy (CONT_IND is A)are not affected by the PAI programme, and map tiles that only contain data surveyed at 1:10 000 scale accuracy (CONT_IND is C) are not affected either.

The following is extracted from the Land Line user guide v5.2 04/2004

Content indicator values

The content indicator (also known as a capture standard) in the map header gives an overview of the scale of the source map from which the data was digitised initially, and a guide to the standards of survey that have been used to maintain the data subsequently. Hence, a dual accuracy file will generally contain data digitised from a 1:2500 scale source with some subsequent revision added using survey methods appropriate to 1:1250 scale mapping.
The following list details the meanings of the various alphanumeric strings that may occur in the {CONT_IND} field of the map header.

Value	Description
<S>	Default. No capture standard information.
A	1:1250 scale accuracy standards (complete cover).
B	1:2500 scale overhaul accuracy standards (complete cover).
C	1:10 000 scale accuracy standards (complete cover).
R	1:2500 scale resurvey or reformed (including PAI).
nnC	1:10 000 scale accuracy standards, where nn is a value in the range 00–25 and indicates the number of km² of map detail (the blank areas of the map being available at 1:1250 or 1:2500 scales).

The presence of more than one value indicates multi-accuracy, for example:

Value	Description
AB	Detail captured to both 1:1250 and 1:2500 scales accuracy standards.
BC	Detail captured to both 1:2500 and 1:10 000 scales accuracy standards.
RBC	Detail captured at 1:2500 scale overhaul, 1:2500 scale resurvey and 1:10 000 scale accuracy standards.

. NOTE: Where all four types of survey occur, the code ABC is used.

Only 1:2500 scale data is being addressed under PAI, but what happens to those tiles that have a mix of scales (dual accuracy)?

Please click here to see the answer in the General FAQ section.

How will I identify the improved maps and features in Land-Line?

Please click here to see the answer in the Land-Line FAQ section.

Which OS MasterMap® areas are affected?

The geographic area affected by PAI is the same whether you are a Land Line customer or an OS MasterMap customer. However, since OS MasterMap is a seamless dataset and not supplied as National Grid map tiles, customers will have to identify the PAI-affected area in a different way. To identify the geographic areas affected by PAI, customers can load the map tile listing (Link to PAI map tile listing now available) into their geographical information system (GIS) to identify which of their geographic area is affected, and refer to the programme maps (Link to Maps page) to view the PAI status of their area.

How will I identify the improved maps and features in OS MasterMap?

Please click here to see the answer in the OS MasterMap FAQ section.

How does PAI affect my organisation?