Meridian™ 2 guidance notes

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Introduction

These guidance notes provide guidance on the appearance of maps created from Meridian 2, and on the data itself. They pick out some major aspects of Meridian 2, as described in the Ordnance Survey's Meridian 2 User Guide, but also highlight several issues that are not adequately explained in the User Guide.

More details on some aspects of Meridian 2 can be found in the User Guide which can be downloaded from here. The User Guide also includes details of the use of NTF and DXF to supply the data.

Meridian 2 is an unusual dataset which combines some very detailed elements (roads, alignment of administrative boundaries) with some very generalised elements (urban areas) and some elements with an intermediate amount of detail (railways, coastline). Meridian 2 is an updated version of Meridian. The update has made two significant improvements to the original dataset:

• the whole product was updated in 2001.
• it now includes data for woodlands or water features.

Meridian 2 is used in Digimap to make District View maps, in conjunction with Land-Form PANORAMA.

Feature codes

This table lists the feature codes used in Meridian 2 in numerical order, together with their attributes. The attributes listed are different in some cases from the attributes listed by Ordnance Survey in their User Guide, and are based on EDINA's experience of using the data.

Features codes, or layer names, in Meridian 2 DXF data are prefixed by the characters "G805". For more information on DXF data download the user guide.

This list of feature codes can also be viewed ordered by category.

Attributes

Administrative boundaries

Meridian 2 includes a set of administrative boundaries, depicting counties, districts and unitary authorities. These boundaries are continuous: that is to say, where an administrative boundary coincides with another linear feature (road, railway or urban boundary) both features exist in the data, following the same alignment. The only exception to this is along the coastline, where the administrative boundary feature does not exist, and the administrative area is delimited by the coastline.

Each coastline feature has either the LC and LD attributes or the RC and RD attributes. The attributes that are present refer to the land side of the line, and the attributes that are not present refer to the sea side.

The LC and RC attributes contain the value of the PI attribute of the County seeds (Feature Code 6411) for the counties that lie to the left and right of the line with the LC and RC attributes.

The LD and RD attributes contain the value of the PI attribute of the District or unitary authority seeds (Feature Code 6415) for the districts that lie to the left and right of the line with the LD and RD attributes.

The indication of left and right depends only on the direction in which a particular line was digitised. There is no consistency as to whether the lines forming the boundary of a polygon have been digitised in a clockwise or an anticlockwise direction. This means that left and right are used simply to distinguish one side of the line from the other.

Where unitary authorities have been introduced, the unitary authority's name is supplied as the NM attribute of the District or unitary authority seed (Feature Code 6415). The County seed (Feature Code 6411) is still present, but has an NM attribute of "NON COUNTY". This applies throughout Wales and Scotland, but not in England. No unitary authorities in England are included in Meridian 2.

Road and railway intersections

Where roads cross using a bridge, or a road and a railway cross using a bridge, Meridian 2 does not include information about which is on the bridge and which is under the bridge. Within Digimap, a convention is used where the feature appearing first in the following list is drawn crossing above the other.

• Motorway
• A road
• B road
• Unclassified road
• Railway

This may sometimes give the incorrect impression of the situation on the ground. For example, even if a minor road crosses a motorway on a bridge, the motorway will be drawn on top of the minor road. This has been done since there is no way of identifying the correct arrangement of such features from the data.

Railways

Passenger and freight railways are shown in Meridian 2. This has changed from the original Meridian data.

Water and woodland

Meridian 2 contains polygons depicting lakes and woodland areas sourced from the Strategi product. Additional water features in the data are rivers, classified into large, medium and small and canals.

Urban areas

Meridian 2 contains polygons depicting urban areas, which within the Ordnance Survey User Guide are called Developed Land Use Areas or DLUAs. These polygons are the same as the urban polygons included in the Strategi data, and District View maps in Digimap.

Names

Only three types of feature are named in Meridian 2: urban areas, water features and railway stations. In each of these cases, the name is present in two separate forms. Firstly, the name is present as cartographic text (Feature Code 6551 for urban area names,Feature Code 6552 for water text and Feature Code 6500 for railway station names). Secondly, these names are present as the PN attribute of urban area seeds (Feature Code 6310) and of railway stations (Feature Code 6155).

Unfortunately, there are some names which appear as cartographic text, but not as attribute text, and others for which the opposite is true. In Digimap we use the cartographic text for display purposes. This means that those names which are included only as attribute text are not displayed on District View maps in Digimap.

Topological information

Meridian 2 includes information about how features are connected to others, known as topological information. This information comprises points known as nodes which are positioned at the ends and junctions of linear features. Where a linear feature crosses from one Meridian 2 tile to another, there is a node at the point where the linear feature crosses the edge of the tile with a distinctive feature code.

In Meridian 2, separate topological information is included for roads (node Feature Codes 3500, 3501), for railways (node Feature Codes 6730, 6731), for urban areas (node Feature Codes 6720, 6721), for administrative areas (node Feature Codes 6710, 6711), for water features (node Feature Codes 6770, 6773), water areas (node Feature Codes 6771, 6772), woodland areas (node Feature Codes 6750, 6751) and for the coastline (node Feature Codes 6740, 6741).

In Meridian 2, the other aspect of topological information is that boundaries defining area features (urban areas and administrative areas) are continuous: that is to say, where a boundary coincides with another linear feature (road, railway or another boundary), both features exist separately in the data (each with the appropriate feature code), following the same alignment. This includes where an urban area meets the "neat line" along the edge of the Meridian 2 tile. The only exception to this is along the coastline, where the administrative boundary feature does not exist, and the administrative area is delimited by the coastline.

Neat line

Meridian 2 is supplied in tiles covering 10km x 10km. The boundary of the tile is known as the neat line, and is included in the data as a series of lines with a feature code of 6800. Each of these lines has either the LC and LD attributes, or the RC and RD attributes depending on their direction, in a similar fashion to coastline.

Where the neat line cuts through an urban area, an additional line feature appears in the same location with a feature code of 6801.

Update and new specification

Meridian 2 was created in 2001, and has been compiled from the following datasets: