Difference between revisions of "OR/19/024 Technical information"

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Revision as of 10:08, 8 January 2020

3.1 SCALE The buried valley suite of data was produced for use at 1:250 000 scale providing 250 m ground resolution.

3.2 FIELD DESCRIPTIONS Each buried valley theme (GIS map layer) contains a series of attribute fields specific to the data they contain. For example, the historic buried valleys include a reference field identifying the data source. Table 1 describes the Buried Valleys (onshore) Historic data (centrelines and margins); whilst Table 2 lists the contents of the Modelled Thickness of Buried Valleys theme.


Table 1 Attribute table field descriptions for Buried Valleys (onshore) Historic centrelines and Buried Valley Historic margins.

FIELD NAME FIELD TYPE DESCRIPTION REFERENCE Text The reference from which the data was drawn from FEATURE Text The name of the dataset: e.g. Buried Valley Historic centrelines SCALE Text The scale used to prepare the digital data: e.g. 250000 for 1:250 000 VERSION Text Version number and attribute level of the digital data: e.g. v1.0

Table 2 Attribute table field descriptions for Buried Valleys (onshore) Modelled Thickness of Buried Valleys theme

FIELD NAME FIELD TYPE DESCRIPTION FEATURE Text The name of the dataset: e.g. Buried Valley Historic centrelines THICKNESS Text Thickness of superficial deposits based on a computer interpolation SCALE Text The scale used to prepare the digital data: e.g. 625000 for 1:625 000 VERSION Text Version number and attribute level of the digital data: e.g. v1.0


3.3 EXPLANATION OF THE DATA

3.3.1 Historic references to Buried Valleys The Buried Valley Historic centrelines and Buried Valley Historic margins GIS layers contain the references from which the data they contain was mined. In some instances, different references interpret the same features differently. In cases of multiple interpretations no judgement has been made and all interpretations are included. This enables the user to visualise the diversity of interpretations (Figure 2) and obtain a rudimentary understanding of uncertainty of their location. For full details see Kearsey et al. 2019. Buried Valleys (onshore) Version 1 - (OR/19/003)



Figure 2. Multiple interpretations of the position of a set of buried valley margins. The colours pick out different interpreations of the locations of the positions of the features. Contains NEXTMap™ Britain elevation data from Intermap Technologies. Created using ArcGIS. Copyright © Esri. All rights reserved.


3.3.2 Modelled Thickness of Buried Valleys Modelled Thickness of Buried Valleys is captured from open access borehole records contains the contoured thickness of superficial deposits. These features are grouped in the 5 different categories based on a computer interpolation. The categories are as follows: • 10m – 20 m • 20m – 30 m • 30m – 40 m • Greater than 40 m The ‘Greater than 40 m’ category includes features to a maximum thickness of 161 m of superficial deposits. Buried Valleys are defined as features centred on five or more boreholes containing 20 m or more of superficial deposits. Locations which failed to meet either one of these criteria were removed from the data. For full details see Kearsey et al. 2019. Buried Valleys (onshore) Version 1 (OR/19/003)


3.4 COVERAGE Data covers the known locations of buried valleys across Great Britain


Figure 3. The coverage of the Buried Valley data. Contains Ordnance Data © Crown Copyright and database rights 2019. Ordnance Survey Licence no. 100021290. Created using ArcGIS. Copyright © Esri. All rights reserved.

3.5 DATA FORMAT The Buried Valley suite of data has been created as vector polygons. The data are available in a range of GIS formats, including ArcGIS (.shp), ArcInfo Coverages and MapInfo (.tab). More specialised formats may be available but may incur additional processing costs.

3.6 LIMITATIONS • The Buried Valleys (onshore) suite of data has been developed at 1:250 000 scale and must not be used at larger scales. All spatial searches against the data should therefore be conducted using a minimum 250 m buffer. • Buried Valley (onshore) data described here represents a baseline of BGS’ current understanding of the locations of buried valleys onshore in Great Britain. This information is based on our currently held historical literature and borehole data. It is inevitable that some of the information may in the light of further evidence be deemed incorrect, and require revision or rejection. This data will form the basis of future research into these features and as a consequence will be periodically updated to include new information as it becomes available. • Buried Valleys (onshore) data should only be used as an indicator where evidence has pointed to the presence of a buried valley. However, the absence of evidence does not substantiate the absence of buried valley features. • Buried Valleys (onshore) data contains multiple interpretations as no judgement has been made and all interpretations are included. This enables the user to visualise the diversity of interpretations and obtain a rudimentary understanding of uncertainty of their location. • The Historic Buried Valley data covers only known areas where research has been carried out and published. In other words it is an empirical dataset and this aspect of the dataset will evolve as additional material is identified or published. • Coverage of the modelled thickness of buried valleys is limited to areas where the source data is available for processing. • For a full discussion of the assumptions and limitation of the Buried Valley data see Kearsey et al. 2019. Buried Valleys (onshore) Version 1 (OR/19/003).

References