[Gvsig_english] Re: Definition query

[ernesto sferlazza]

Hi Wolfang & Developers & All
Actually when I work with ESRI ArcGIS Desktop (but the same occurred with
ESRI ArcView 3.x) I use "definition query" on a theme even in editing and in
analysis sessions, not only for viewing purposes.
The advantages of my way or working are (the list is not exaustive):
1) minimize the redundancy of the geographic archive: I can connect to a
unique theme in the geographic archive and each time work with a different
subset (that I can save as a layer file). The consequent advantage is that
if  I update the original theme there is no need of updating any exported
theme. This behaviour is very important for me, since in my Administration
the GIS archive is unique and structured (folder, subfolders, etc., with
metadata per each folder explaining semantically the themes archivied into
it) and many projects (or maps, using ESRI) refers to this unique archive.
2) Sometimes I could have the need of symbolizing a theme on more than one
attribute, e.g. the first one qualitative (owner: Provincia, Stato, Comune),
the second one quantitative (numbers of vehicles per day). With a definition
query I can create different "virtual" themes based on the owner and then
simbolize each theme clissifying the volume of traffic.
3) for particular purposes (e.g. managing the "time dimension") I need to
consider only features that satisfy a query on particular attributes storing
the "born date" and the "death date" of the feature. In this case, useful
for example for themes regardin town planning, I can store in the same theme
all the history of the theme itself. (for more details see :
http://www.provincia.agrigento.it/flex/cm/pages/ServeAttachment.php/L/IT/D/D.1ca591e5be2fe39a9071/P/BLOB%3AID%3D26


Best regards
-- 
ing. Ernesto Sferlazza
responsabile nodo provinciale di Agrigento del SITR Sicilia
resp. U.O. Sistema Informativo Territoriale
Provincia regionale di Agrigento
sede istituzionale: piazza Aldo Moro, 1 - 92100 AGRIGENTO
sede operativa: via Acrone, 27 - 92100 AGRIGENTO
cell. 3392718463
tel. uff 0922401935
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