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GIS Guide to Good Practice |
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5.3 Information to be recorded
It is generally a good idea to start recording information about your data
as early as possible, and ideally you should begin recording as soon as you
start using or creating the data. If you wait until just before depositing
with ADS to start creating metadata and documentation, it will be difficult
for you to provide some pieces of information at all, and far harder to write
most of the rest than it would have been at the time you were actually
doing it. Assuming that you choose to record relevant details as you go along, it might
be useful for you to start a formal log book of some kind. This way, it will
be easier to find information later, rather than having to rifle through
various old envelopes, scrap paper, and whatever else you scribbled on at the
time. Within this log book, it is normal to record such general details as the
software you are using, the versions thereof, and the type of computer (PC,
Macintosh, Sun workstation, etc. rather than Dell, Viglen, Compaq,
etc.) you are running it on. As time passes, people discover problems
with earlier versions of software, and if someone finds out that
SuperGIS version 23.7 displaced all green lines on maps by 3mm, then
it is undoubtedly useful for you to be able to look back through the log book
and find that all your maps displaying public rights of way were created
three years ago using SuperGIS 23.7. Knowing there is a
problem, you can do something about retrospectively fixing it with adequate
documentation. Information about where the data you use are acquired from is one of the most
important things you can record whilst constructing and using a GIS. Data are acquired from numerous sources, including
Ordnance Survey and other
mapping agencies, local authorities, special interest groups, etc.,
and are gathered and displayed at a wide variety of often different
scales or resolutions. Each of these sources are of value for a different set of purposes, and each
brings with it a different set of problems; data acquired at 1:50,000 scale,
for example, may be ideally suited for plotting maps of artefact distributions,
but wholly improper for recording the layout of individual excavation trenches
(1 centimetre on a 1:50,000 map, after all, is equivalent to 50,000
centimetres, or 500 metres, on the ground). In order to aid the user in deciding how best to incorporate your data within
their own work, it is desirable to provide them with information such as the
scale or resolution of the original survey, scale or resolution at which that
survey was digitised into the computer, assumed errors from the data capture
process (often expressed as a Root Mean Square, or
RMS, error on printed maps),
and the method by which the data were originally acquired (although both
ultimately plotted at a scale of 1:100, a user will presumably be interested
to know that one topographic data set was constructed by survey with measuring
tapes and dumpy level, whilst the other is the result of a detailed survey by
state of the art Total Station Theodolite). Ownership of data is also an important attribute to record about any data set,
and may well prove quite complex. Data owned by the
Ordnance Survey, for example,
might be used by North Yorkshire County Council to derive a new data set,
'owned' by the County Council. This, in turn, is used by York Archaeological
Trust to derive a new data set, now 'owned' by them. Although little, if any,
of the original Ordnance Survey resource may survive in this latest
incarnation of the data, Ordnance Survey in reality continue to hold
intellectual property rights which should be recognised and which may well
affect the ease with which, for example, York Archaeological Trust could later
legally sell 'their' data to Yorkshire Water. Complicated data trails such as this are extremely common with digital data,
and it makes life easier for everyone if the evolution of every data set is
tracked through every reincarnation. In short, then, a nonexhaustive list of the information you might
wish to record during your everyday creation, collection, and use of data
includes: As well as recording information such as that suggested above, most of which will probably only need recording once when you start work with a data set, it is also extremely valuable to log the manner in which data are manipulated and modified. Not only does this allow you to keep track of and backtrack from, if necessary changes you make to the data, but it also allows you and others to work out how data you lifted from your local Sites & Monuments Record, for example, and incorporated into your own GIS differs from those same records still residing in the SMR. How many records have you enhanced? For how many have you had to reenter the grid references, as you discovered that those provided by the SMR actually placed sites in the North Sea? The sorts of information you may wish to consider logging for these purposes include:
Where you edit an existing data set to correct spelling in text fields, or some similar operation, it makes more sense to simply record this as 'Corrected spelling throughout data set' and give the numbers of those records altered if relevant, rather than to list every single correction made to every single record. For processes such as converting an elevation matrix to a Triangulated Irregular Network (TIN) or an equally drastic data set-wide modification, it is worth recording the parameters you used in undertaking this process so that you and others may repeat or undo it in the future. |
The right of Mark Gillings, Peter Halls, Gary Lock, Paul Miller, Greg Phillips, Nick Ryan, David Wheatley, and Alicia Wise to be identified as the Authors of this Work has been asserted by them in accordance with the Copyright, Designs and Patents Act 1988. All material supplied via the Arts and Humanities Data Service is protected by copyright, and duplication or sale of all or part of any of it is not permitted, except that material may be duplicated by you for your personal research use or educational purposes in electronic or print form. Permission for any other use must be obtained from the Arts and Humanities Data Service(info@ahds.ac.uk). Electronic or print copies may not be offered, whether for sale or otherwise, to any third party.
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