tion may involve hundreds of data sets that are combined for a single inter-
pretation of how multiple factors influence each other.
Accuracy refers to the degree of correspondence between data and the actual
thing or event. Reliability indicates how consistent the data is for certain
types of applications. Usually high accuracy means high reliability, but in sev-
eral circumstances the opposite may be the case.
First, data may be highly accurate, but because of the time between its
collection and its analysis, it may no longer be reliable. Aerial photos and sat-
ellite imagery can easily become dated and will vary greatly from the actual
situation. Second, reliable data may have a low accuracy. For example, data
showing the major roads in the United States may be useful for reliably
determining how to go from Boston to San Diego, but not accurate enough
for determining how far a recycling center in San Diego is located from a
The balance between accuracy and reliability is often a financial issue.
Because of the high costs of data collection, often limitations for both accu-
racy and reliability are acceptable. The key points about this balances is first
to clearly describe the data's date of collection and concerns about possible
discrepancies to the actual situation and, second, to take these discrepancies
into account when analyzing the data.
Basic Geographic Information Analysis Types and Applications
Solely as an overview of the many types of geographic information analysis
and applications, this section gives some insight into pragmatic issues and
applications of geographic information analysis. These geographic informa-
tion analysis operations only partially correspond to GIS operations and
commands. Depending on the software's analytical capabilities, the analysis
in GIS may involve a single command or many commands. Because of the
endless permutations of geographic information analysis operations, a
direct match to any single GIS software's set of operations and commands
only makes sense for specific applications and domains.
People who have worked with maps may think of the geographic information
query in terms of interactive maps. In its simplest form, geographic informa-
tion querying involves both spatial and attribute aspects allowing for a per-
son to select a feature and find out its attributes. In many applications, the
programming of the interface can make this a very helpful feature to find
out the name of lakes, cities, clinics, or restaurants. Even for professional
geographic information analysis, geographic information querying is often
important in determining attributes of individual features. Related to the