Glossary
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Administrative area map level
A map definition level of a virtual map. It describes the planning
and operational areas used in daily municipal operations. Boundary
lines for administrative areas generally follow street segments, but
may cut street or even parcel boundaries at times. Each administrative
area definition is established independent of the other; rarely will
any two sets of districts be the same. The map stores descriptive
and digital boundary identifications that can be related to facility,
legal and base geography area definitions as required. Examples of
administrative area definitions are: census tracts, health districts,
police beats or districts, fire response areas, planning districts,
transportation zones, etc.
Business data needs
Businesses typically need street data to locate customers for helping
customer profiling and visualizing customer locations in relation
to competitors. Business tasks often require demographic or consumer
data to identify new markets, define sales territories, or select
the product mix that should be offered at a particular retail/business
outlet. Knowing how to invest advertising dollars is heavily dependent
upon the demographic composition of different areas. Business tasks
include advertising planning, competitive analysis, customer profiling,
defining sales territories, demographic analysis, employee recruitment,
fund raising, market share analysis, market potential assessment,
merchandising mix, new product development, optimal routing, promotion/event
planning, property management, referral services, resource allocation,
site selection, telemarketing campaigns.
Continuous space
To be most effective, the GIS allows storage of map features and attributes
in a spatially continuous format over a specific geographic area (e.g.,
city, county, service area, state). Such an approach frees the user
from having to access and analyze information on a map-sheet by map-sheet
basis. Information for any geographic area, large or small, can be
extracted, queried, and analyzed. Carried to its full extent, a continuous
spatial database has no "seams" or boundaries that represent
physical or logical file breaks in the storage of GIS data.
Digital elevation model
The digital cartographic representative of the surface of the Earth
or a subsurface feature through a series of three-dimensional coordinate
values: a continuous variable over a two-dimensional surface by a
regular array of z values referenced to a common datum. Digital elevation
models are typically used to represent terrain relief; a model of
terrain relief in the form of a matrix consisting of a data file of
a topographic surface arranged as a set of regularly spaced X,Y,Z
coordinate locations where Z represents surface elevation. Abbreviated
DEM. The grid is defined by identifying one of its corners (lower
left usually), the distance between nodes in both the X and Y directions,
the number of nodes in both the X and Y directions, and the grid orientation.
Discontinuous surface
A surface type with the characteristic of having different z values
at a given x,y location on the surface as approached from different
directions, e.g., discontinuous surface is a vertical fault on the
surface of the Earth. A location at the top of the fault has one elevation,
but immediately below this point at the bottom of the fault another
elevation is observed. A model capable of storing a discontinuous
surface must be able to store more than one z value for a given x,y
location.
Dynamic segmentation
A GIS function for modeling linear features in highway applications
such as accident analysis and pavement management. The process has
the ability to compute locations of events on linear features at run
time (or dynamically) in linear measure (e.g. milepost). Event features,
the segmentation points, are not stored in the geometry of the coverage
but are derived as needed. Route-system features and event handling
commands provide the dynamic segmentation capability within GIS systems
to dynamically locate events on linear features that are obtained
from attribute tables of events for which distance measures are available.
Both point and linear events can be located on routes; lane closure
is an example of a linear event and the accident location is an example
of a point event.
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