panorama guidance

Land-Form PANORAMA® guidance notes

Introduction

These guidance notes provide guidance on the appearance of maps created from Land-Form PANORAMA Contours and guidance on the Contour and Digital Terrain Model (DTM) versions of the Land-Form PANORAMA data. Ordnance Survey produce a User Guide for these products which can be downloaded from here. The User Guide also includes details of the use of NTF and DXF to supply the data.

Both Land-Form PANORAMA Contours and Land-Form PANORAMA DTM have been created from the contours that appear on the Landranger^® (1:50,000 scale) map series. They are each very different ways of presenting height information. These guidance notes are therefore structured into two separate sections, one for Contours, and one for DTM.

All heights in Land-Form PANORAMA are given in metres above mean sea level (or more precisely, above Ordnance Survey's reference datum, which was mean sea level at Newlyn in Cornwall measured from 1 May 1915 to 30 April 1921).

The Land-Form PANORAMA products are not updated, and were created in November 1993.

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

Land-Form PANORAMA® Contours

General

Land-Form PANORAMA Contours contain line features and point features. The line features depict Contours, Lakes, Breaklines, Coastlines, Ridge Lines and Form Lines. The point features depict Spot Heights.

Contours and Lakes from Land-Form PANORAMA are used to create District View maps in Digimap, in conjunction with Ordnance Survey's Meridian product.

Instances of each feature type carry a numeric attribute giving a height to the nearest metre. In the case of Coastline this height is 0m. Some Form Lines in low-lying terrain (for instance in Norfolk) have negative values.

Land-Form PANORAMA Contours contain no cartographic text (i.e. text designed for display on screen). The height attribute associated with each feature can be used for display purposes.

Accuracy

The height accuracy of contours is 3 metres (standard error). That is to say, if you were to accurately measure the height at a point on the ground that lies on a contour, then that height would be within 3m of the value given for the contour 68% of the time. Spot heights values are published to the nearest metre.

Feature Codes

The Land-Form PANORAMA Contour data contains seven feature types. Each of these is given a Feature Code which is a text string made up of four digits. Features codes, or layer names, in Land-Form PANORAMA Contour and Land-Form PANORAMA DTM DXF data, are prefixed by the characters "G804" and "G810" respectively. For more information on DXF data download the user guide. The complete list of Feature Codes for Contour data and a description of what they refer to is given here:

Feature Code	Description	Type	Attributes	Notes
0200	Spot Height	Point	HT	Height measured at a given point. Spot Heights are usually located at the top of hills.
0201	Contour	Line	HT	A line connecting points of equal height or elevation. Contours are at 10m vertical intervals.
0202	Lake	Line	HT	Bodies of inland water, including ponds, lakes, lochs and the lower parts of some rivers. See below for explanation.
0203	Breakline	Line	HT	A line indicating a discontinuity in the terrain surface, e.g. an abrupt change in gradient. See below for discussion.
0204	Coastline	Line	HT	Mean High Water along coast, including tidal estuaries.
0205	Ridge Line	Line	HT	A line marking where the direction of the gradient changes at the top of a ridge, or at the base of a valley.
0207	Form Line	Line	HT	A supplementary contour, used for two purposes, detailed below.

The attribute code used above is detailed in the table below.

Code	Description	Notes
HT	Height	Height of feature in metres.

By inspection of the data, many instances of Ridge Lines and Breaklines appear to be incorrectly coded as Form Lines.

Contours (Feature Code 0201)

Contours are depicted as two dimensional lines, with the HT attribute giving the contour's height in metres. The contours are at a vertical interval of 10m.

Contours (Feature Code 0201) in Land-Form PANORAMA Contours are discontinuous in many places. This generally occurs in 6 different cases:

areas of steep ground where it was impossible to draw all contours continuously on the 1:50,000 scale map without the contour lines touching. In this case, contours whose height attribute is a multiple of 50m are continuous, while other contours are likely to be broken. These contours are known as index contours and are drawn with a heavier line on the published map. Examples are contours for 50m, 100m, 150m etc.
coastal cliffs and reservoir dams. These are special cases of the situation described above, where index contours may also be discontinuous. The line of a reservoir dam is sometimes depicted by a Breakline (Feature Code 0203).
major road and railway cuttings and embankments
areas of sand dunes where Ordnance Survey have not surveyed the contours. In this case, the two ends of the discontinuous contour are often joined using a Form Line (Feature Code 0207), to assist visual interpretation of the shape of the ground. In these cases the Form Line's height attribute will be a multiple of 10m.
areas where man-made workings have changed the contours. This includes quarries and opencast mine workings. In this case, the two ends of the discontinuous contour are usually joined using a Form Line (Feature Code 0207) to indicate where the ground level lay before the quarrying activity took place. In these cases the Form Line's height attribute will be a multiple of 10m. In some cases the top edge of the quarry working is marked with a Breakline (Feature Code 0203).
tile boundaries. Land-Form PANORAMA Contours are produced in 20km x 20km tiles. When a contour reaches a tile edge, it sometimes continues from a slightly different point on the boundary of the neighbouring tile.

Lakes (Feature Code 0202)

Each feature coded as a Lake includes a height attribute (HT), giving the elevation of the water surface.

The Lake feature code (0202) is used for the lower stretches of some major rivers, above the tidal limit. (Below the tidal limit, the Coastline feature code (0204) is used.) Rivers are portrayed in this way in cases where the two banks of the river are wide enough apart to be shown separately. When this is done, the river is divided up arbitrarily into a series of polygons where each polygon is given a separate height. Therefore, on the lower part of a river, below the 10m contour, there will be a water polygon with a height attribute of 9m, another polygon with a height attribute of 8m, and so on. Unfortunately, there are small gaps between each successive polygon.

Where a body of water contains an island, then the island has the same Feature Code (0202) as the body of water.

Breaklines (Feature Code 0203)

Breaklines are sometimes used to depict the line of the top of a reservoir dam, or the top of a quarry. In each of these cases, the Breakline has a height attribute (HT) of 0m, regardless of its true height.

Ridge Lines (Feature Code 0205)

Ridge lines depict the line of the top of a ridge, or the base of a valley. There are very few ridge lines included in the Land-Form PANORAMA dataset: they are generally only present on ridges where the location of the top of the ridge may not be clear from the surrounding contours. They are more frequently used to depict the base of valleys. Unfortunately, many ridge lines are (incorrectly) coded as Form Lines (Feature Code 0207).

In some areas in south-eastern Devon and Portland in Dorset (tiles SS80, SX86, SX88, SY68), the use of ridge lines is completely different from the rest of PANORAMA, and a very complete network of ridge lines is shown.

Form Lines (Feature Code 0207)

Form Lines are used for two purposes in Land-Form PANORAMA Contours.

As supplementary contours at a height which falls between contours at the normal vertical interval, usually used to indicate the direction or shape of a particular feature (e.g. valley or ridge) where the normal contours do not give such an indication. In these cases the Form Line's height attribute will not be a multiple of 10m.
Where contours cross quarries or areas of sand dunes, the contours are sometimes broken. In these cases, a Form Line is used to join the two ends of a contour in order to assist visual interpretation of the shape of the ground, and in the case of quarries, to indicate where the ground level lay before the quarrying activity took place. In these cases the Form Line's height attribute will be a multiple of 10m.

Land-Form PANORAMA® Digital Terrain Model (DTM)

General

Land-Form PANORAMA Digital Terrain Model (DTM) contains height information only. It does not contain a representation of the Spot Heights, Lakes, Coastline or other features that are represented in Land-Form PANORAMA Contours.

Heights are given at the intersections of a horizontal 50 metre grid. Each height is given to the nearest 1 metre. These values have been mathematically interpolated from the same set of features that are represented in Land-Form PANORAMA Contours.

The height is given across all areas of the grid, including sea and other water areas, and including areas (such as quarries and sand dunes) where the contours in Land-Form Contours are discontinuous.

Accuracy

The accuracy of the heights in the DTM is 5 metres. That is to say, if you were to compare height on the ground with the stated height in the DTM for a particular location, the two values would agree within 5m. This is a greater error margin than found in the Land-Form PANORAMA Contour data, because the interpolation process used to create the DTM from the contour data introduces another possible source of error.