Information and Advisory Note Number 104
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Further development of the inventory of ancient and
long-established woodland sites and the semi-natural woodland inventory
1. Introduction
The main objective of this work was to produce updated versions of the two
Inventories (in digital and hardcopy formats) for use by SNH staff and others.
The purpose of this I & A note is to record the status and methodology used to
produce Version 2 of the Inventories.
The work comprised five distinct components and was completed in the stages
outlined in Figure 1 and discussed below:
2. Development of procedure for data
checking and correction
Discrepancies were identified by the contractors who produced the digital
version (MLURI) (Anderson 1995; MLURI 1996) within the digital Inventories.
Codes describing each type of discrepancy were recorded (polygon by polygon) in
the digital version. These codes were subsequently prioritised according to
their severity and appropriate corrections were undertaken.
2.1 Assignation of error codes by MLURI
During the production of the digital version of the Inventories the range of
logical errors which occurred were recorded within the master dataset.
These error codes fell into five categories ('map' refers to an individual 10 km
square map sheet) and it was considered necessary to correct those described
below:
REM_4: Within map coding errors
40 - polygon uncoded, attached to adjacent site
41 - Polygon uncoded, unable to identify coding
REM_5: Within map hatching/ boundary errors
REM_6: Between map boundary/ coding errors
60 - Unmatched boundary, polygon or part of polygon closed at map edge
61 - Unmatched boundary, boundary extended from/to the adjoining map: boundary
added at checking stage
62 - polygon boundary/ coding carried across to/from the adjoining map
63 - Unmatched origin, polygon closed at map edge
REM_8: Between map miscellaneous errors
80 - possible error or omission in comment entries
2.2 Categorisation of error severity
At the start of this project the error codes were categorised according to their
severity, with more severe errors given a higher priority for correction (Table
1)
Figure 1: Project structure
Table 1 Severity codes
(Note: only polygons of 2 hectares or greater were checked during the correction
process the original minimum resolution of the Inventories).
REM_5 errors relating to the semi-natural inventory were ignored because it is
anticipated that the semi-natural inventory will be superseded within the next
two years by a revised and updated inventory currently under compilation by the
LIFE Caledonian Partnership.
3. Checking and correction of errors in the Inventory of Ancient and
Long-established Woodland Sites and the Semi-Natural Woodlands Inventory.
3.1 Production of materials for error checking
A0 map printouts of the inventory were produced in two formats: one with the
errors shaded according to severity; and one with all woodland polygons shaded
according to their antiquity. These maps were used in conjunction with the
original paper-based inventory maps and printed lists of errors for error
checking in the map library of the National Library of Scotland. The edge_jd
item in the inventory polygon records was used to cross-reference between maps
and printed lists.
3.2 Error checking from the source maps in the National Library of Scotland
The source maps used for the correction of errors at the National Library were
the Roy Military Survey of Scotland (c. 1750) and the first edition Ordnance
Survey maps (c. 1850). Depending upon the nature of the error either, or both
map sources were consulted. The original OS 1:25000 maps (c. 1970s) also used in
the compilation of the inventory were also available within SNH. Any changes to
polygon boundaries or coding were marked on the paper inventory maps, with
additional comments noted in the printed lists. (These reference maps and papers
are stored in Forestry and Woodlands Branch.)
3.3 Error correction and assignation of correction codes
The processes of error checking and correction of the digital inventory were
undertaken concurrently. A copy of the original digital inventory coverage was
split into ten smaller coverages to facilitate faster processing (particularly
for building topology and drawing the coverages). The coverages were split using
the 100-kilometre square names, e.g. NM, NO etc.. This method avoided the
division of individual polygons but required care when altering boundaries at
the edges of 100-kilometre squares in case of conflict when the coverages were
reassembled. It also had the advantage of highlighting polygons which had been
given incorrect square attributes (and so were distant from the other polygons
in the coverage).
Coding corrections to the digital Inventory attribute table were made using the
UPDATE command in either INFO or TABLES. Boundary corrections were made within
ArcEdit using the appropriate OS 1:50000 map image as a backdrop for context.
All checked polygons (whether corrected or uncorrected) were assigned a code in
the REM_9 column, which had previously been added to the inventory attribute
table (Table 2).
Table 2: REM_9 correction codes
In the first two-thirds of the error checking process at the National Library of
Scotland all high and medium severity errors were checked and corrected,
together with approximately half of the low severity errors. As time allowed,
the remainder of the scattered low severity errors were corrected, as well as
the larger errors (over approximately 10 ha.) related to hatching boundary
errors (REM_7). These hatching errors were corrected using stereo pairs of the
SDD 1:24 000 aerial photography inventory.
3.4 Final checking of the corrected coverage When all errors had been checked
and corrected as necessary the 100-kilometre square coverages were reassembled
into a single coverage using the MAPJOIN command. Any remaining boundary error
conflicts between 100-kilometre squares were resolved, the entire coverage for
Scotland was cleaned and the topology was re-built.
During the error correction process there were alterations to the values of the
wood_id item, which was originally a unique woodland identifier. These values
were recalculated by 10-kilometre square. This item can then be used to link
individual woodland polygons on the paper maps to the record in the inventory.
3.5 Redefinition of Antiquity The antiquity woodland categories were then
redefined so that the following codes applied (table 3). Two new items,
Antiquity (the woodland type definition) and Antiquity_id (the woodland type
code) were added to the inventory records This brought the Scottish inventories
broadly into line with that of England and Wales, where antiquity is defined by
presence on the first edition Ordnance Survey maps. It also took account of
uncertainties during compilation, particularly those associated with the Roy
maps. The original codes are still available in the orig_id field (Kupiec 1997).
Table 3: Antiquity Woodland Categories
4. Data description
During the correction process only one master copy of the Inventories was used,
and all alterations were made to this. The two Inventories produced for general
release were reselected from this master dataset. We retained the majority of
the fields from version 1 in the master copy and the two separated Inventories
used a sub-set of this. The fields available in the different copies of the
Inventory are set down in Table 4.
5. Release of the Inventory of Ancient and Long-established Woodland Sites and
the Semi-Natural Woodland Inventory Version 2.0.
5.1 Digital copy
Version 2.0 of each digital inventory is now ready for general release. This
will be accompanied by a document detailing the background and nature of the
inventory. The Inventory of Ancient and Long-established Woodland Sites and the
Semi-Natural Woodland Inventory will be made available separately. Overlay and
interrogation of the two Inventories within a GIS will be a relatively simple
process.
5.2 Hardcopy
The inventories will also be available for general use in hardcopy form as paper
maps. These will be in the form of A4 printouts of each 10-kilometre square,
with an OS 1:50000 backdrop to add context to the Inventory printouts.
6. Analysis
A variety of standard analyses were undertaken for both
Inventories to produce standard results for general use. In particular the
distribution of ancient, semi-natural woodland was analysed by National Heritage
Zones, Local Authority Areas, Protected Areas and SNH Areas. There was a
comparison between the extent of woodland contained in the Inventories and the
woodland classes contained in the LCS88 dataset.
Table 4 The Data Fields in the master copy of the Inventories
7. References
Anderson, H. 1995. Digital Capture of the Ancient Woodland Inventory (Cairngorms
Area). Final Report to Scottish Natural Heritage. Research Contract: SNH/091/95
(Cairngorms).
Kupiec, J. 1997. The inventory of ancient and long-established woodland sites
and the inventory of semi-natural woodlands (provisional). Information and
Advisory Note No. 95. Scottish Natural Heritage, Perth.
Macaulay Land Use Research Institute 1996. Creating a Geographic Information
System of The Ancient and Semi-natural Woodland Inventory. Research Contract:
SNH/091/95.
8. Authors
John Kupiec (on behalf of Scottish Natural
Heritage)
Amanda Thomson, Forestry and
Woodlands, Scottish Natural Heritage
Caroline Younger, Forestry and
Woodlands, Scottish Natural Heritage
9. Contact for further information
Forestry and Woodlands GIS/Database
Manager
Forestry and Woodlands Branch
Scottish Natural Heritage
2 Anderson Place
EDINBURGH
EH6 5NP
Tel: 0131-447 4784
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