Geography Reference
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of your plans could be contracted to a consulting firm for checking. However it is done, someone other
than the originators of the techniques for development of information from data should independently
examine the projected course of action.
4. Begin the data acquisition effort with a pilot project.
So far, I have described a rather idealized process for the formation of a portion of a database for a GIS. I
think the idealized approach is worth sticking to. Too many times the existence of some collected datasets
not only dictates the process used to manipulate them but also the kinds of products that get produced.
It often turns out that when the cost of conversion of already collected data is counted, the error rate
discovered, and the lack of suitability of the data for the task at hand realized, more money and time will
have been spent than if an original data collection effort were begun. And yet, it is unreasonable not to
make an examination of existing data sources, after you know what you want, to see if, considering the
millions spent on data collection in this country, there are some data sets that will meet your needs.
(a) A search for relevant data may not prove easy. Although there are myriad Web sites that allow
downloads (paid or free), the questions of appropriateness and quality will keep occurring. It may
be the type of frustrating undertaking during which one never really knows when to surrender; how
long do you keep looking before you elect another route? A common problem is that very few peo-
ple seem to have both the depth of understanding required to manipulate data into information in
particular areas and the overall view of how to collect the data that could be relevant to the decision-
making process.
A real search, therefore, should be undertaken, and it should look widely, not eschewing any possible
source of data. Interviewing of individuals in various agencies and companies is probably as profitable
as searches through documents on the Web; interviews may produce more up-to-date information about
data sources or data collection efforts.
There is no dearth of data, spatial or otherwise, but there are three major problems with existing data:
(1) The data files themselves are spatially distributed, hither and yon, in offices and computing centers,
in desk drawers and filing cabinets. Perhaps the first task in developing data for a specific
geographic area should be a list that includes data sources, characteristics, and owners.
(2) The data sets are not in a common format. Granted, different sorts of data should be presented in
different form because of their inherent characteristics and uses, but the variability vastly exceeds the
requirements for different formats.
(3) Already existing datasets are getting older and less correct every day. The accuracy of the data will
decay slowly over time.
A method for assessing the correctness of data after a length of time might be borrowed from the concept
in physics of a radioactive half-life period. Such a period, measured in time units (from millionths of a
second to years to millennia) and different for each radioactive substance, is the length of time required for
half the mass of the substance to have decayed into something else. In general form this idea could have
a parallel with “correctness of a set of data” as the variable instead of mass of material. The correctness of
spatially distributed data of a given type, say, land use, decays at different rates depending, as you might
imagine, on its location. A greater rate of decay would be expected adjacent to urban areas than distant
from them. In any event, the age of the data used is one of its most important characteristics.
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