Geography Reference
In-Depth Information
Geoserver project, enabling it to directly extract both polygons and statistical data from
our Oracle data. So far, statistical mapping is limited to the
rates
defined in the DDS, and
Figure 13.5 shows one of the resulting pages, slightly edited to save space. The map itself
is an utterly unremarkable choropleth map of population growth rates, but the range of
options the system is offering the user demonstrates its flexibility:
The timeline bar above the map allows the user to request a map for a different date.
Dates for which the same map cannot be drawn are greyed out, but this particular
map requires only the most basic population count so it is available for every census
year except the very first, 1801. The same timeline appears above time series graphs
of the rate, and is used to request a map.
Zoom in, zoom out and, hopefully, pan are self-explanatory even with a general
audience. They are unlikely to have used even desktop GIS software, but Multimap,
Streetmap and various on-line route planning sites should make these tools familiar.
Choosing 'Select Unit' enables users to go to our 'home page' for the particular
administrative unit they next click on.
Once they start zooming in, few people can tell where they are looking at on a
map consisting entirely of administrative boundaries. Another part of the project
scanned three complete sets of historical one inch to one mile maps of Britain, plus
less detailed maps from roughly the same dates. This material is held in a separate
repository but is accessible using the Open Geospatial Consortium's Web Map Server
standard. We present it independently in our 'historical mapping' section, but it is
also available as an underlay for the statistical mapping, the statistical mapping
servlet calling the historical WMS.
The next set of options is the various rates which are available within the same
theme for the same date and type of unit. An obvious limitation of this interface
is that it does not show what additional rates might be available if the user changes
the date or unit type.
Finally, the user can request a map of the same rate for the same date but a different
type of administrative unit. This particular map is an extreme case, because the 1911
census reported both on the nineteenth century system of Registration Counties
and Districts as well as the then-new local government geography. The units actually
being used in this map are modern district and unitary authorities, based on our
redistricting work. The parish-level geography is greyed out but will become an
option once the user zooms in sufficiently.
The greatest virtue of this system is how easily extensible it is: adding a whole new set of
maps requires nothing more than a new rate definition within the DDS.
13.4.2 Graphing nCubes
The most easily accessible graphs in the system are also based on rates, presenting time series
for the selected unit and an additional 'comparison unit'. By default, these comparisons are
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