John Wood said
>If we are dealing with polygons, what sort of symbols are we
>talking about?
Remembering that the depiction is dependent on and secondary to feature
classification, then there are many types of polygons in archaeological data -
for example, a post-hole, a survey area, an excavation trench, a scheduled area,
an area within which an artefact is thought to have been found, an area within
which a reported monument may be located, a 'mapped' monument (e.g. the
triumphal arch), an area enclosing geophysical anomalies, etc.etc. These types
of feature have to be distinguished somehow (and it is more than a question of
precision/confidence).
Peter Iles message has just arrived confirnming this point!
There are also many legitimate types of line, point, grid/lattice, and volume(!)
features in archaeological data.
Consensus so far has been that it is this issue that could be very usefully
addressed by new content and terminology standards (as additions to MIDAS and
INSCRIPTION for example), and that this could remove one of the big problems in
current handling and exchange of digital spatial archaeological data. Spatial
feature type standards do exist already, but they don't cater for the wierder
types of feature that may be unique to archaeology.
Can we can agree on the following ?
- we *need* content and terminology *standards* for spatial feature types;
- it would be *useful* to develop *conventions* on how to depict these feature
types for certain common purposes (such as print publication, Local Plan
mapping) and this process should probably involve designing ways of implementing
the conventions within certain proprietory software systems.
Cheers
Crispin
______________________________ Reply Separator _________________________________
Subject: Re: Standard symbologies
Author: "The Forum for Information Standards in Heritage (FISH)"
<[log in to unmask]> at Internet
Date: 03/10/01 10:12
Bob has prompted me to contribute as folows:
Our SMR makes extensive use of ArcView and I see there is huge potential in
GIS to do much more than we currently manage.
However, perhaps I have missed a point somewhere? The most useful aspect of
the GIS is its capacity to store and display polygons. Unfortunately most
of our data is still represented by points - plotted grid references. This
is a legacy from our development from card index to database but we need to
move beyond this stage as soon as possible. If we are dealing with
polygons, what sort of symbols are we talking about? While we certainly
want a useful, common language that is easily recognised and understood by
all, those demanding standard 'symbologies' need to be very clear about what
the objective is and why people should adopt the standards.
I certainly don't support a standard data structure - this seems to me to
have more potential for restricting innovation and imaginative systems
development than any positive benefit. What matters is the product not the
process.
Bob says,
"There are some challenges in the database design process - notably, how to
render features with ambiguous geometries, or at different scales. Is a
triumphal arch a point feature or an area feature? Is a long narrow shell
midden a line, an area, or a point? What if the midden was recorded in 1940
as a circle on a map of the coastline?"
All these are area features and can be represented as polygons. Designated
areas (listed buildings, scheduled monuments) are defined, but beyond this,
to some extent, all archaeological sites and features have ambiguous
boundaries. Surely we just need a field in the theme table that indicates
an ambiguity value, just as we and others are currently implementing with
our point data. Users could be provided with a scale from 1 to 10 (say)
which provided an assessment of the polygon's accuracy. Different scales
should not be a problem with a GIS!
Are we in danger of seeing problems where none really exist?
John Wood
----------------------------------------------------------
John Wood
Senior Archaeologist
Planning and Development Service
The Highland Council
Glenurquhart Road
Inverness IV3 5NX
Tel: 01463 702502 Fax: 01463 702298
Email: [log in to unmask]
Web: <http://www.higharch.demon.co.uk>
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