Geography Reference
In-Depth Information
hundreds of statistical tables within the Oracle database matched the units defined in the
label points. In many ways, this system was a triumph of making software do something it
was not designed for, but it was almost impossible to ensure data integrity and it was clearly
too slow to drive a high volume web site (Gregory and Southall, 1998).
New funding from the UK national lottery, discussed below, forced a major rethink
leading to a completely new architecture in which almost everything was held in Oracle,
ArcGIS playing no role. This would have been impossible when we started in 1994 because
it requires a relational database with object extensions, enabling spatial data to be held
alongside statistics and text. Figure 13.1 provides an overview, although it ignores how we
hold text and historical maps.
The original GBH GIS had been able to create maps, using ArcMap, but it required users
to select a particular statistical table from an ever-growing collection of many hundreds, and
then to choose sensible combinations of columns from those tables to compute a rate. Our
new approach began by saying that we were interested in the individual data values, and it
was actively unhelpful to group them into 'tables' which generally came from census reports
and each held data from a single year. Instead, we would hold
all
statistical data values in a
single column of just one table, and give them meaning entirely through metadata.
Our main
data table
is almost as simple as Figure 13.1 suggests: one column holds the
data values themselves and then other columns hold values recording location, meaning,
date and source. The date column in fact holds an object, able to hold anything from a single
calendar year, for a census, to a pair of calendar dates, e.g. for quarterly mortality data.
The other columns hold identifiers whose meanings are defined in the three main metadata
sub-systems.
Where
is recorded not by any kind of coordinate data but by a reference to a
large
Administrative Gazetteer
of over 50 000 British local government units, modern and
historical, each of which can have a set of associated variant names and, if available, one
or more boundary polygons, using dates on the polygons to handle change over time. A
central aim was to create a system which could hold information for units whose location
was either unknown or had yet to be recorded through the expensive process of boundary
digitization. Units are grouped into
Unit types
which have some of the characteristics of
Where?
Gazetteer
Source?
What?
Data
Documentation
System
Source
Documentation
System
DDS
Data
When?
Date Object
Figure 13.1
GB Historical GIS: overview
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