OR/14/029 Model datasets used - Revision history

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	{{Template:OR/14/029}}		{{Template:OR/14/029}}
	__NOTOC__		__NOTOC__
	The model covers eight 1:50 000 scale England & Wales series geological map sheets: 254 (Henley-on-Thames), 255 (Beaconsfield), 256 (North London), 257 (Romford), 268 (Reading), 269 (Windsor), 270 (South London) and 271 (Dartford); together with thin small portions of a further 14 1:50 000 scale map sheets: 238 (Aylesbury), 239 (Hertford), 240 (Epping), 241 (Chelmsford), 253 (Abingdon), ~~258-259~~ (Southend and Foulness), 267 (Hungerford and Newbury), 272 (Chatham), 283 (Andover), 284 (Basingstoke), 285 (Guildford), 286 (Reigate), 287 (Sevenoaks) and 288 (Maidstone). These 1:50 000 scale map sheet areas are named and their extents are shown in blue in Figure 3, with the Area 1–12 tiles outlined in red.		The model covers eight 1:50 000 scale England & Wales series geological map sheets: 254 (Henley-on-Thames), 255 (Beaconsfield), 256 (North London), 257 (Romford), 268 (Reading), 269 (Windsor), 270 (South London) and 271 (Dartford); together with thin small portions of a further 14 1:50 000 scale map sheets: 238 (Aylesbury), 239 (Hertford), 240 (Epping), 241 (Chelmsford), 253 (Abingdon), 258–259 (Southend and Foulness), 267 (Hungerford and Newbury), 272 (Chatham), 283 (Andover), 284 (Basingstoke), 285 (Guildford), 286 (Reigate), 287 (Sevenoaks) and 288 (Maidstone). These 1:50 000 scale map sheet areas are named and their extents are shown in blue in Figure 3, with the Area 1–12 tiles outlined in red.

	[[Image:029_fig2.jpg\|thumb\|center\|600px\|'''Figure 3''' 1:50 000 scale geological map sheets corresponding to the model.]]		[[Image:029_fig2.jpg\|thumb\|center\|600px\|'''Figure 3''' 1:50 000 scale geological map sheets corresponding to the model.]]

Dbk at 10:26, 10 August 2015

2015-08-10T10:26:56Z

← Older revision		Revision as of 11:26, 10 August 2015
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	{{Template:OR/14/029}}		{{Template:OR/14/029}}
	__NOTOC__		__NOTOC__
	The model covers eight 1:50 000 scale England & Wales series geological map sheets: 254 (Henley-on-Thames), 255 (Beaconsfield), 256 (North London), 257 (Romford), 268 (Reading), 269 (Windsor), 270 (South London) and 271 (Dartford); together with thin small portions of a further 14 1:50 000 scale map sheets: 238 (Aylesbury), 239 (Hertford), 240 (Epping), 241 (Chelmsford), 253 (Abingdon), 258-259 (Southend and Foulness), 267 (Hungerford and Newbury), 272 (Chatham), 283 (Andover), 284 (Basingstoke), 285 (Guildford), 286 (Reigate), 287 (Sevenoaks) and 288 (Maidstone). These 1:50 000 scale map sheet areas are named and their extents are shown in blue in Figure 3, with the Area ~~1-12~~ tiles outlined in red.		The model covers eight 1:50 000 scale England & Wales series geological map sheets: 254 (Henley-on-Thames), 255 (Beaconsfield), 256 (North London), 257 (Romford), 268 (Reading), 269 (Windsor), 270 (South London) and 271 (Dartford); together with thin small portions of a further 14 1:50 000 scale map sheets: 238 (Aylesbury), 239 (Hertford), 240 (Epping), 241 (Chelmsford), 253 (Abingdon), 258-259 (Southend and Foulness), 267 (Hungerford and Newbury), 272 (Chatham), 283 (Andover), 284 (Basingstoke), 285 (Guildford), 286 (Reigate), 287 (Sevenoaks) and 288 (Maidstone). These 1:50 000 scale map sheet areas are named and their extents are shown in blue in Figure 3, with the Area 1–12 tiles outlined in red.

	[[Image:029_fig2.jpg\|thumb\|center\|600px\|'''Figure 3''' 1:50 000 scale geological map sheets corresponding to the model.]]		[[Image:029_fig2.jpg\|thumb\|center\|600px\|'''Figure 3''' 1:50 000 scale geological map sheets corresponding to the model.]]
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	==Boreholes==		==Boreholes==

	Borehole information was downloaded from the BGS Intranet Data Portal, which automatically generates GSI3D-ready model files. The ''bid ''file contains the location information of each borehole (easting, northing and start height) and the ''blg ''file holds the downhole information recorded in the BGS Borehole Geology (BoGe) database. On completion of any borehole coding needed the bid and blg files were downloaded on a tile by tile basis.		Borehole information was downloaded from the BGS Intranet Data Portal, which automatically generates GSI3D-ready model files. The ''bid ''file contains the location information of each borehole (easting, northing and start height) and the ''blg ''file holds the downhole information recorded in the BGS Borehole Geology (BoGe) database. On completion of any borehole coding needed the bid and blg files were downloaded on a tile by tile basis.

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	In total, 7174 borehole logs were considered in cross-section construction (Figure 4), comprising both confidential and open access borehole data, plus geotechnical boreholes that were absent from the BGS Single Onshore Borehole Index (SOBI). During the project assembly a GIS was used to ensure an even distribution of coded boreholes wherever possible, and additional boreholes were selected for coding from the BGS Borehole Geology database to infill the data poor areas. Selection criteria were drilled depth, borehole location and level of detail in the borehole log. Deeper boreholes were selected preferentially to constrain the deepest geological units, such as the top Chalk surface. The quality of the logs themselves was also important. For example, a recently drilled borehole with a detailed log was selected preferentially over an old log conveying scant information. Old water wells were particularly difficult to use as they often prove the depth of the top Chalk surface, but provide no information on the thickness or composition of overlying units.		In total, 7174 borehole logs were considered in cross-section construction (Figure 4), comprising both confidential and open access borehole data, plus geotechnical boreholes that were absent from the BGS Single Onshore Borehole Index (SOBI). During the project assembly a GIS was used to ensure an even distribution of coded boreholes wherever possible, and additional boreholes were selected for coding from the BGS Borehole Geology database to infill the data poor areas. Selection criteria were drilled depth, borehole location and level of detail in the borehole log. Deeper boreholes were selected preferentially to constrain the deepest geological units, such as the top Chalk surface. The quality of the logs themselves was also important. For example, a recently drilled borehole with a detailed log was selected preferentially over an old log conveying scant information. Old water wells were particularly difficult to use as they often prove the depth of the top Chalk surface, but provide no information on the thickness or composition of overlying units.

	Boreholes were coded in the BGS Borehole Geology database using the content code ‘LS’ (London Strategic Model), which identifies coding specific to this project. To standardise the borehole coding, the superficial deposits coding scheme (Cooper et al. 2006) was used, where single letter codes represent the main lithologies (boulders are represented by the letter B, L is for cobbles, V for gravel, S for sand, C for clay, Z for silt and P for peat). For mixed compositions, the main lithology is coded first, with additional lithologies added to the right in order of decreasing proportion. An example of how the codes can be applied to increasingly mixed lithologies is shown in Table 5. In this scheme, almost any combination of the letter codes is permissible.		Boreholes were coded in the BGS Borehole Geology database using the content code ‘LS’ (London Strategic Model), which identifies coding specific to this project. To standardise the borehole coding, the superficial deposits coding scheme (Cooper et al. 2006<ref name="Cooper">COOPER, A H, KESSLER, H and FORD, J R. 2006. A revised scheme for coding unlithified deposits (also applicable to engineering soils). ''British Geological Survey Internal Report'' IR/05/123 </ref>) was used, where single letter codes represent the main lithologies (boulders are represented by the letter B, L is for cobbles, V for gravel, S for sand, C for clay, Z for silt and P for peat). For mixed compositions, the main lithology is coded first, with additional lithologies added to the right in order of decreasing proportion. An example of how the codes can be applied to increasingly mixed lithologies is shown in Table 5. In this scheme, almost any combination of the letter codes is permissible.


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	==Digital terrain model (DTM)==		==Digital terrain model (DTM)==
			All individual model tiles used a DTM in ASCII grid format, sub-sampled from the superseded 5 m resolution CEH DTM or the later, also superseded, 5 m NextMap DTM. These DTM extracts were downloaded via the BGS Intranet Data Portal and were converted to TINs within the GSI3D project to cap each model. Tiles 1–6 initially used a DTM with a cell size of 25 m, and tiles 7–12 were constructed using a 50 m DTM.
	All individual model tiles used a DTM in ASCII grid format, sub-sampled from the superseded 5 m resolution CEH DTM or the later, also superseded, 5 m NextMap DTM. These DTM extracts were downloaded via the BGS Intranet Data Portal and were converted to TINs within the GSI3D project to cap each model. Tiles ~~1-6~~ initially used a DTM with a cell size of 25 m, and tiles ~~7-12~~ were constructed using a 50 m DTM.

	The combined model is now capped by a BGS produced Bald Earth DTM with a 100 m cell size. This DTM is based on the same NextMap DTM as before but with Ordnance Survey Landform Profile data inserted for extensive wooded areas as the NextMap DTM was found to be unreliable in these locations, it often depicted the top of the tree canopy rather than the actual ground surface.		The combined model is now capped by a BGS produced Bald Earth DTM with a 100 m cell size. This DTM is based on the same NextMap DTM as before but with Ordnance Survey Landform Profile data inserted for extensive wooded areas as the NextMap DTM was found to be unreliable in these locations, it often depicted the top of the tree canopy rather than the actual ground surface.

	==Legacy and other 3D model data==		==Legacy and other 3D model data==

	===Thames Gateway models===		===Thames Gateway models===
	Tiles 2, 3, 5 and 6 overlap pre-existing unapproved LithoFrame 10 Thames Gateway 3D models (shown as the blue hatched area in Figure 5). In tiles 2, 3, and 5, the Thames Gateway model data was not incorporated but was replaced by the London Basin model.		Tiles 2, 3, 5 and 6 overlap pre-existing unapproved LithoFrame 10 Thames Gateway 3D models (shown as the blue hatched area in Figure 5). In tiles 2, 3, and 5, the Thames Gateway model data was not incorporated but was replaced by the London Basin model.
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	In the east, the London Basin Model overlaps with higher resolution models including, Farringdon, Lower Lea Valley, Thames Flood Prevention, Thames Flood Defence, Tilbury Docks, and ALF Archaeology. It also adjoins a model for Cliffe at Hoo, Kent. These models were not taken into account in the London Basin model, and in some cases (e.g. Farringdon) they post-date the basin wide model and were built using its existing cross-sections as a framework.		In the east, the London Basin Model overlaps with higher resolution models including, Farringdon, Lower Lea Valley, Thames Flood Prevention, Thames Flood Defence, Tilbury Docks, and ALF Archaeology. It also adjoins a model for Cliffe at Hoo, Kent. These models were not taken into account in the London Basin model, and in some cases (e.g. Farringdon) they post-date the basin wide model and were built using its existing cross-sections as a framework.

	There are also two bedrock models referred to as the Inner London Chalk Project (Royse et al. 2010) and Cray-Swanscombe Project that do not include superficial deposits. The former includes a subdivision of the Chalk Group, which was beyond the scope of the current basin model.		There are also two bedrock models referred to as the Inner London Chalk Project (Royse et al. 2010<ref name="Royse">ROYSE, K , KESSLER, H., ROBINS, N., HUGHES, A..& MATHERS, S. 2010 [http://nora.nerc.ac.uk/10139/ The use of 3D geological models in the development of] [http://nora.nerc.ac.uk/10139/ the conceptual groundwater model.] ''Zeitschrift der Deutschen Gesellschaft für Geowissenschaften'', 161 (2). 237–249 doi\|10.1127/1860-1804/2010/0161-0237 </ref>) and Cray-Swanscombe Project that do not include superficial deposits. The former includes a subdivision of the Chalk Group, which was beyond the scope of the current basin model.

	The eastern half of the London Basin model coincides with the LOCUS model developed by BGS in the mid 1990s, the new model supersedes it but makes use of some of the borehole coding undertaken for this earlier study.		The eastern half of the London Basin model coincides with the LOCUS model developed by BGS in the mid 1990s, the new model supersedes it but makes use of some of the borehole coding undertaken for this earlier study.

	==Artificial ground representation==		==Artificial ground representation==

	Artificial ground was already recorded on some 1:50 000 scale map sheets in the model area, but not on others. To address these inconsistencies a GIS-based desk study was carried out to identify instances of artificial ground that were not present in the DiGMapGB-50 or -10 datasets. This involved examining modern 1:10 000 scale topographic maps for areas where the ground surface has been artificially modified, such as in embankments and cuttings along transport routes, reservoirs, etc. At the same time, the existing DiGMap artificial ground data was validated, including the resolution of mismatches across original map sheet boundaries, these were corrected in the model. However, the Artificial Ground categories are excluded from the model calculation because, although they are mapped as coverages in x and y dimensions, there is insufficient data in the model to constrain the base of these deposits (z) and so produce a calculated volume. To date this updated artificial ground information has not been incorporated into the currently released version of DiGMapGB-50.		Artificial ground was already recorded on some 1:50 000 scale map sheets in the model area, but not on others. To address these inconsistencies a GIS-based desk study was carried out to identify instances of artificial ground that were not present in the DiGMapGB-50 or -10 datasets. This involved examining modern 1:10 000 scale topographic maps for areas where the ground surface has been artificially modified, such as in embankments and cuttings along transport routes, reservoirs, etc. At the same time, the existing DiGMap artificial ground data was validated, including the resolution of mismatches across original map sheet boundaries, these were corrected in the model. However, the Artificial Ground categories are excluded from the model calculation because, although they are mapped as coverages in x and y dimensions, there is insufficient data in the model to constrain the base of these deposits (z) and so produce a calculated volume. To date this updated artificial ground information has not been incorporated into the currently released version of DiGMapGB-50.

	==Data collation==		==Data collation==
			A GSI3D project workspace was set up for each of the model tiles, each contained data relevant to that particular area. This included clipped national DiGMapGB-50 polygon data, a DTM with a cell size of 25 m (in tiles 1–6) or 50 m (tiles 7–12) to cap the model, and the relevant borehole data files. The boreholes, DTM and DiGMapGB-50 polygons were also buffered to include data from slightly outside the tile area in order to provide contextual information. This buffered area also provided data to help constrain the base of geological units in the absence of corresponding data near the edge of a tile.

	A GSI3D project workspace was set up for each of the model tiles, each contained data relevant to that particular area. This included clipped national DiGMapGB-50 polygon data, a DTM with a cell size of 25 m (in tiles 1–6) or 50 m (tiles 7–12) to cap the model, and the relevant borehole data files. The boreholes, DTM and DiGMapGB-50 polygons were also buffered to include data from slightly outside the tile area in order to provide contextual information. This buffered area also provided data to help constrain the base of geological units in the absence of corresponding data near the edge of a tile		==References==

	[[Category:OR/14/029 The London Basin superficial and bedrock LithoFrame 50 model\| 04]]		[[Category:OR/14/029 The London Basin superficial and bedrock LithoFrame 50 model\| 04]]

Dbk at 16:15, 11 March 2015

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Dbk: Protected "OR/14/029 Model datasets used" ([Edit=Allow only administrators] (indefinite) [Move=Allow only administrators] (indefinite)) [cascading]

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Protected "OR/14/029 Model datasets used" ([Edit=Allow only administrators] (indefinite) [Move=Allow only administrators] (indefinite)) [cascading]

← Older revision	Revision as of 16:41, 11 March 2015
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← Older revision		Revision as of 10:24, 10 March 2015
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			{{Template:OR/14/029}}
	__NOTOC__		__NOTOC__
	The model covers eight 1:50 000 scale England & Wales series geological map sheets: 254 (Henley-on-Thames), 255 (Beaconsfield), 256 (North London), 257 (Romford), 268 (Reading), 269 (Windsor), 270 (South London) and 271 (Dartford); together with thin small portions of a further 14 1:50 000 scale map sheets: 238 (Aylesbury), 239 (Hertford), 240 (Epping), 241 (Chelmsford), 253 (Abingdon), 258-259 (Southend and Foulness), 267 (Hungerford and Newbury), 272 (Chatham), 283 (Andover), 284 (Basingstoke), 285 (Guildford), 286 (Reigate), 287 (Sevenoaks) and 288 (Maidstone). These 1:50 000 scale map sheet areas are named and their extents are shown in blue in Figure 3, with the Area 1-12 tiles outlined in red.		The model covers eight 1:50 000 scale England & Wales series geological map sheets: 254 (Henley-on-Thames), 255 (Beaconsfield), 256 (North London), 257 (Romford), 268 (Reading), 269 (Windsor), 270 (South London) and 271 (Dartford); together with thin small portions of a further 14 1:50 000 scale map sheets: 238 (Aylesbury), 239 (Hertford), 240 (Epping), 241 (Chelmsford), 253 (Abingdon), 258-259 (Southend and Foulness), 267 (Hungerford and Newbury), 272 (Chatham), 283 (Andover), 284 (Basingstoke), 285 (Guildford), 286 (Reigate), 287 (Sevenoaks) and 288 (Maidstone). These 1:50 000 scale map sheet areas are named and their extents are shown in blue in Figure 3, with the Area 1-12 tiles outlined in red.
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	==Data collation==		==Data collation==

	A GSI3D project workspace was set up for each of the model tiles, each contained data relevant to that particular area. This included clipped national DiGMapGB-50 polygon data, a DTM with a cell size of 25 m (in tiles 1–6) or 50 m (tiles 7–12) to cap the model, and the relevant borehole data files. The boreholes, DTM and DiGMapGB-50 polygons were also buffered to include data from slightly outside the tile area in order to provide contextual information. This buffered area also provided data to help constrain the base of geological units in the absence of corresponding data near the edge of a tile~~.{{Template:OR/14/029}}~~		A GSI3D project workspace was set up for each of the model tiles, each contained data relevant to that particular area. This included clipped national DiGMapGB-50 polygon data, a DTM with a cell size of 25 m (in tiles 1–6) or 50 m (tiles 7–12) to cap the model, and the relevant borehole data files. The boreholes, DTM and DiGMapGB-50 polygons were also buffered to include data from slightly outside the tile area in order to provide contextual information. This buffered area also provided data to help constrain the base of geological units in the absence of corresponding data near the edge of a tile

	[[Category:OR/14/029 The London Basin superficial and bedrock LithoFrame 50 model\| 04]]		[[Category:OR/14/029 The London Basin superficial and bedrock LithoFrame 50 model\| 04]]

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	==Data collation==		==Data collation==

	A GSI3D project workspace was set up for each of the model tiles, each contained data relevant to that particular area. This included clipped national DiGMapGB-50 polygon data, a DTM with a cell size of 25 m (in tiles 1–6) or 50 m (tiles 7–12) to cap the model, and the relevant borehole data files. The boreholes, DTM and DiGMapGB-50 polygons were also buffered to include data from slightly outside the tile area in order to provide contextual information. This buffered area also provided data to help constrain the base of geological units in the absence of corresponding data near the edge of a tile.		A GSI3D project workspace was set up for each of the model tiles, each contained data relevant to that particular area. This included clipped national DiGMapGB-50 polygon data, a DTM with a cell size of 25 m (in tiles 1–6) or 50 m (tiles 7–12) to cap the model, and the relevant borehole data files. The boreholes, DTM and DiGMapGB-50 polygons were also buffered to include data from slightly outside the tile area in order to provide contextual information. This buffered area also provided data to help constrain the base of geological units in the absence of corresponding data near the edge of a tile.{{Template:OR/14/029}}

	[[Category:OR/14/029 The London Basin superficial and bedrock LithoFrame 50 model\| 04]]		[[Category:OR/14/029 The London Basin superficial and bedrock LithoFrame 50 model\| 04]]

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	Artificial ground was already recorded on some 1:50 000 scale map sheets in the model area, but not on others. To address these inconsistencies a GIS-based desk study was carried out to identify instances of artificial ground that were not present in the DiGMapGB-50 or -10 datasets. This involved examining modern 1:10 000 scale topographic maps for areas where the ground surface has been artificially modified, such as in embankments and cuttings along transport routes, reservoirs, etc. At the same time, the existing DiGMap artificial ground data was validated, including the resolution of mismatches across original map sheet boundaries, these were corrected in the model. However, the Artificial Ground categories are excluded from the model calculation because, although they are mapped as coverages in x and y dimensions, there is insufficient data in the model to constrain the base of these deposits (z) and so produce a calculated volume. To date this updated artificial ground information has not been incorporated into the currently released version of DiGMapGB-50.		Artificial ground was already recorded on some 1:50 000 scale map sheets in the model area, but not on others. To address these inconsistencies a GIS-based desk study was carried out to identify instances of artificial ground that were not present in the DiGMapGB-50 or -10 datasets. This involved examining modern 1:10 000 scale topographic maps for areas where the ground surface has been artificially modified, such as in embankments and cuttings along transport routes, reservoirs, etc. At the same time, the existing DiGMap artificial ground data was validated, including the resolution of mismatches across original map sheet boundaries, these were corrected in the model. However, the Artificial Ground categories are excluded from the model calculation because, although they are mapped as coverages in x and y dimensions, there is insufficient data in the model to constrain the base of these deposits (z) and so produce a calculated volume. To date this updated artificial ground information has not been incorporated into the currently released version of DiGMapGB-50.

	== ~~name="_TOC_250020"~~ ==		==Data collation==

	A GSI3D project workspace was set up for each of the model tiles, each contained data relevant to that particular area. This included clipped national DiGMapGB-50 polygon data, a DTM with a cell size of 25 m (in tiles 1–6) or 50 m (tiles 7–12) to cap the model, and the relevant borehole data files. The boreholes, DTM and DiGMapGB-50 polygons were also buffered to include data from slightly outside the tile area in order to provide contextual information. This buffered area also provided data to help constrain the base of geological units in the absence of corresponding data near the edge of a tile.		A GSI3D project workspace was set up for each of the model tiles, each contained data relevant to that particular area. This included clipped national DiGMapGB-50 polygon data, a DTM with a cell size of 25 m (in tiles 1–6) or 50 m (tiles 7–12) to cap the model, and the relevant borehole data files. The boreholes, DTM and DiGMapGB-50 polygons were also buffered to include data from slightly outside the tile area in order to provide contextual information. This buffered area also provided data to help constrain the base of geological units in the absence of corresponding data near the edge of a tile.







	[[Category:OR/14/029 The London Basin superficial and bedrock LithoFrame 50 model\| 04]]		[[Category:OR/14/029 The London Basin superficial and bedrock LithoFrame 50 model\| 04]]

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	The eastern half of the London Basin model coincides with the LOCUS model developed by BGS in the mid 1990s, the new model supersedes it but makes use of some of the borehole coding undertaken for this earlier study.		The eastern half of the London Basin model coincides with the LOCUS model developed by BGS in the mid 1990s, the new model supersedes it but makes use of some of the borehole coding undertaken for this earlier study.

	== ~~name="_TOC_250021"~~ ==		==Artificial ground representation==

	Artificial ground was already recorded on some 1:50 000 scale map sheets in the model area, but not on others. To address these inconsistencies a GIS-based desk study was carried out to identify instances of artificial ground that were not present in the DiGMapGB-50 or -10 datasets. This involved examining modern 1:10 000 scale topographic maps for areas where the ground surface has been artificially modified, such as in embankments and cuttings along transport routes, reservoirs, etc. At the same time, the existing DiGMap artificial ground data was validated, including the resolution of mismatches across original map sheet boundaries, these were corrected in the model. However, the Artificial Ground categories are excluded from the model calculation because, although they are mapped as coverages in x and y dimensions, there is insufficient data in the model to constrain the base of these deposits (z) and so produce a calculated volume. To date this updated artificial ground information has not been incorporated into the currently released version of DiGMapGB-50.		Artificial ground was already recorded on some 1:50 000 scale map sheets in the model area, but not on others. To address these inconsistencies a GIS-based desk study was carried out to identify instances of artificial ground that were not present in the DiGMapGB-50 or -10 datasets. This involved examining modern 1:10 000 scale topographic maps for areas where the ground surface has been artificially modified, such as in embankments and cuttings along transport routes, reservoirs, etc. At the same time, the existing DiGMap artificial ground data was validated, including the resolution of mismatches across original map sheet boundaries, these were corrected in the model. However, the Artificial Ground categories are excluded from the model calculation because, although they are mapped as coverages in x and y dimensions, there is insufficient data in the model to constrain the base of these deposits (z) and so produce a calculated volume. To date this updated artificial ground information has not been incorporated into the currently released version of DiGMapGB-50.

Dbk: /* Other models */

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Other models

← Older revision		Revision as of 13:41, 6 March 2015
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	[[Image:029_fig6.jpg\|thumb\|center\|500px\|The LithoFrame 10 HS2 route model area, shown in blue stipple.]]		[[Image:029_fig6.jpg\|thumb\|center\|500px\|The LithoFrame 10 HS2 route model area, shown in blue stipple.]]

	==Other models==		===Other models===
	In the west, the London Basin Model overlaps with bedrock models for the Berkshire Downs, the Goring Gap, and the Itchen. These do not include significant components of superficial deposits but were considered in the bedrock geology interpretation.		In the west, the London Basin Model overlaps with bedrock models for the Berkshire Downs, the Goring Gap, and the Itchen. These do not include significant components of superficial deposits but were considered in the bedrock geology interpretation.

Dbk: /* =Other models */

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=Other models

← Older revision		Revision as of 13:40, 6 March 2015
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	[[Image:029_fig6.jpg\|thumb\|center\|500px\|The LithoFrame 10 HS2 route model area, shown in blue stipple.]]		[[Image:029_fig6.jpg\|thumb\|center\|500px\|The LithoFrame 10 HS2 route model area, shown in blue stipple.]]

	===Other models==		==Other models==
	In the west, the London Basin Model overlaps with bedrock models for the Berkshire Downs, the Goring Gap, and the Itchen. These do not include significant components of superficial deposits but were considered in the bedrock geology interpretation.		In the west, the London Basin Model overlaps with bedrock models for the Berkshire Downs, the Goring Gap, and the Itchen. These do not include significant components of superficial deposits but were considered in the bedrock geology interpretation.

← Older revision		Revision as of 17:15, 11 March 2015
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	The model covers eight 1:50 000 scale England & Wales series geological map sheets: 254 (Henley-on-Thames), 255 (Beaconsfield), 256 (North London), 257 (Romford), 268 (Reading), 269 (Windsor), 270 (South London) and 271 (Dartford); together with thin small portions of a further 14 1:50 000 scale map sheets: 238 (Aylesbury), 239 (Hertford), 240 (Epping), 241 (Chelmsford), 253 (Abingdon), 258-259 (Southend and Foulness), 267 (Hungerford and Newbury), 272 (Chatham), 283 (Andover), 284 (Basingstoke), 285 (Guildford), 286 (Reigate), 287 (Sevenoaks) and 288 (Maidstone). These 1:50 000 scale map sheet areas are named and their extents are shown in blue in Figure 3, with the Area 1-12 tiles outlined in red.		The model covers eight 1:50 000 scale England & Wales series geological map sheets: 254 (Henley-on-Thames), 255 (Beaconsfield), 256 (North London), 257 (Romford), 268 (Reading), 269 (Windsor), 270 (South London) and 271 (Dartford); together with thin small portions of a further 14 1:50 000 scale map sheets: 238 (Aylesbury), 239 (Hertford), 240 (Epping), 241 (Chelmsford), 253 (Abingdon), 258-259 (Southend and Foulness), 267 (Hungerford and Newbury), 272 (Chatham), 283 (Andover), 284 (Basingstoke), 285 (Guildford), 286 (Reigate), 287 (Sevenoaks) and 288 (Maidstone). These 1:50 000 scale map sheet areas are named and their extents are shown in blue in Figure 3, with the Area 1-12 tiles outlined in red.

	[[Image:029_fig2.jpg\|thumb\|center\|600px\|Figure 3 1: 50 000 scale geological map sheets corresponding to the model.]]		[[Image:029_fig2.jpg\|thumb\|center\|600px\|'''Figure 3''' 1:50 000 scale geological map sheets corresponding to the model.]]


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	Where a Borehole Geology database entry already existed for a borehole, it was not re-coded if the level of detail was sufficient for modelling. However, where a borehole only conveyed the depth of Rockhead, it was re-coded to maximise the data available for the 3D model. A selection of borehole logs were coded in areas with a high borehole density because of the sheer number of them, and only the deepest or most detailed logs were selected for coding where clusters occurred.		Where a Borehole Geology database entry already existed for a borehole, it was not re-coded if the level of detail was sufficient for modelling. However, where a borehole only conveyed the depth of Rockhead, it was re-coded to maximise the data available for the 3D model. A selection of borehole logs were coded in areas with a high borehole density because of the sheer number of them, and only the deepest or most detailed logs were selected for coding where clusters occurred.

	[[Image:O29_fig4.jpg\|thumb\|center\|600px\|Figure 4 Location of borehole logs consulted in model construction.]]		[[Image:O29_fig4.jpg\|thumb\|center\|600px\|'''Figure 4''' Location of borehole logs consulted in model construction.]]

	==Digital terrain model (DTM)==		==Digital terrain model (DTM)==
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	In Tile 6, the Thames Gateway cross-sections and envelopes (unit coverages) were retained and extended to the edge of this tile, with the correlation lines reassessed, matched to the 1:50 000 scale map linework and the previously completed model tiles. The stratigraphy of these Thames Gateway cross-sections were simplified to fit the schema of the London Basin model, in particular including the removal of subdivisions within the alluvium. The earlier Thames Gateway project borehole coding was retained and decisions on whether to accept these earlier interpretations were decided on a case by case basis in the context of the revised cross-sections.		In Tile 6, the Thames Gateway cross-sections and envelopes (unit coverages) were retained and extended to the edge of this tile, with the correlation lines reassessed, matched to the 1:50 000 scale map linework and the previously completed model tiles. The stratigraphy of these Thames Gateway cross-sections were simplified to fit the schema of the London Basin model, in particular including the removal of subdivisions within the alluvium. The earlier Thames Gateway project borehole coding was retained and decisions on whether to accept these earlier interpretations were decided on a case by case basis in the context of the revised cross-sections.

	[[Image:029_fig5.jpg\|thumb\|center\|500px\|Figure 5 The Thames Gateway models, shown in blue hatching.]]		[[Image:029_fig5.jpg\|thumb\|center\|500px\|'''Figure 5''' The Thames Gateway models, shown in blue hatching.]]

	===HS2 route model===		===HS2 route model===
	The 1:10 000 scale HS2 route model, commissioned by HS2 Ltd in 2013, adds more detail to the London Basin LithoFrame 50 regional model in tiles 1 and 9. This involved a reinterpretation of borehole data within the HS2 project area (shown in blue shading in Figure 6), which was then incorporated into the London Basin combined borehole files. Extra cross-sections were added into the HS2 area, and these were then incorporated into the London Basin regional model. The superficial deposits correlated in the London Basin model cross-sections were matched to the HS2 cross-sections. The HS2 model conveys greater detail in the anthropogenic deposits than DigMapGB-50, and this was not carried over into the revision of the London Basin model.		The 1:10 000 scale HS2 route model, commissioned by HS2 Ltd in 2013, adds more detail to the London Basin LithoFrame 50 regional model in tiles 1 and 9. This involved a reinterpretation of borehole data within the HS2 project area (shown in blue shading in Figure 6), which was then incorporated into the London Basin combined borehole files. Extra cross-sections were added into the HS2 area, and these were then incorporated into the London Basin regional model. The superficial deposits correlated in the London Basin model cross-sections were matched to the HS2 cross-sections. The HS2 model conveys greater detail in the anthropogenic deposits than DigMapGB-50, and this was not carried over into the revision of the London Basin model.

	[[Image:029_fig6.jpg\|thumb\|center\|500px\|The LithoFrame 10 HS2 route model area, shown in blue stipple.]]		[[Image:029_fig6.jpg\|thumb\|center\|500px\|'''Figure 6''' The LithoFrame 10 HS2 route model area, shown in blue stipple.]]

	===Other models===		===Other models===