GIS glossary: a-g
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GIS glossary: a-g
"A Practitioner's Guide to GIS Terminology"
The following terms are condensed and reproduced with permission from "A Practitioner's Guide to GIS Terminology" by Stearns J. Wood, which contains more than 10,000 terms (see GIS glossary).
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.
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.
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.
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.
earth satellite thematic sensing
Landsat satellites have a Thematic-Mapper (tm) sensor that produces images in many spectral regions, e.g., in the visible range, in the near-infrared, in the mid-infrared, and in the thermal infrared. The visible and near-infrared regions provide information on water turbidity, bathymetry, currents, and sediment plumes. (Water containing large quantities of suspended sediment has a higher reflectance than clear water and can be easily separated using satellite data). The near-infrared band is used for vegetation mapping since it distinguishes features by variations in plant cell structure. Mid-infrared spectral regions reveal plant water content and help delineate vegetation type. Two mid-infrared bands are used for geological studies and one for collecting imagery at night and identifying hot objects, such as forest fires, lava flows, emissions from smoke stacks, new construction, and soil use.
elastic body transformation
A least-squares computer software program run against a raw digitized data source map to produce a geographically true "X" and "Y" coordinate database referenced to any standard map system. Based on the locations of control monuments, a "best fit" is made to the source map's origin, rotation, scale, skew, and stretch. If the source map's systematic errors were small, an accurate "fit" will be made resulting in small residual errors. Also called rubber sheeting and coordinate rotation/translation.
facility area map level
A map definition level of a virtual map. It describes the street, water, sewer, gas, electric, phone and cable networks together with the cumulated structures developed to meet the needs of the people within the land area. The facility area data files describe and define the street network and street facilities of the area with locational coordinates associated with the facilities and supplemental identifiers. The facility definition (street network), when related to spatial display, uses a base geography area definition. A GIS provides a framework for data manipulation and display of map data especially for: (a) location verification, (b) location correlation, (c) locational relationships. (d) district coding. (e) route analysis, (f) area analysis and (g) mapping/display creation.
facilities management system
GIS technology applied to the information in a database pertaining to public or private facilities as utility or engineering facilities, i.e., electrical stations and distribution lines, water reservoirs and distribution lines, natural gas lines distribution, telephone lines distribution, sewer treatment plants and collection lines, streets and roadway systems, etc., of an area having a map reference which has the ability to be represented by symbols and data on the maps drawn by a computer mapping system. The user of the FM system can direct it to select any one pole or facility, or it can access all data poles or facilities in a region, zone, city block or any area designated, regardless of size or shape. It can also cross-reference and access the records of the pole or facility, such as size and type, inventory number, date of installation, date of last inspection (plus results), and other equipment installed on a pole and access the account numbers of the customers whose service drops emanate from a pole.
forest management system
GIS technology applied to providing and maintaining a continuous supply of wood fiber while balancing environmental (e.g., a forest home to whitetail deer, moose, black bears, bald eagles, and other wildlife), social (e.g., thousands of people enjoying the forest area for hiking, rafting the whitewater, fishing and hunting), and regulatory factors. This system provides the means to analyze the land base relative to the amount of wood actually available for harvest, with consideration for applicable regulations. This allows appropriate harvest scheduling and timber supply analysis, e.g., timber volumes by species and product are multiplied by cover type acreages to arrive at estimated inventories.
Regulatory zones for streams, lakes and rivers, and wildlife management are mapped and assessed for their impact on wood supply that allows for keeping track of all diverse demands on the land and the variety of constraints on timber availability. The system includes forest stands, all roads, hydrology and political boundaries, which allows use of the system for management activities such as harvest, planting, vegetation suppression, thinning and road construction.
An abbreviation for Geographic Coding. The procedure for locating and translating geographic coordinates in x,y digits or grid cells for an object or event in space and coded in map units, lines, and points. Geographic information is prepared for input into a computer in particular political subdivisions through the process of cross-referencing points, street addresses and geographic areas, and hence the attributes of those points or areas, by the use of a geographic numbering system, for the assignment of geographic codes (such as census tracts, police districts, zip codes, soil areas, legislative districts) to records of events or data. Geocoding is an essential step in plotting such information on a map in which map coordinates are attached to each data record based on its address.
geographic boundary data
Computer database containing boundaries for areas such as census areas, postal areas and political or administrative areas, area centroids (points used to represent areas) and related associated attribute information such as area names, identification numbers, latitude/longitude coordinates, polygon area calculation, demographics, inventories relating to area, precision of boundary nodes. Geographic boundary data are used for analyzing market potential and penetration, sales territory definition, site selection, neighborhood analysis, market and trend analysis, redistricting, environmental and medical research and analysis, historical studies, school districts, postal carrier zone calculations, zip code area studies, watershed and habitat area analysis.
A collection of data that is individually or collectively attached to geographic location. Spatial data is a term used synonymously with geographic data elements that describe a geographic area (parcels, streets, intersections, railroads, drainage, sidewalks, fences, driveways, buildings, cultural features, as well as coordinates, geographic codes, addresses) that can be displayed in graphic form as maps, drawings, charts, etc. Nominal location identifiers are used to indicate positions in space relative to other data and are typically names or code numbers of geographic entities such as administrative districts, postal zones, street addresses, political subdivisions, rivers, highways, settlements, census tracts, and so forth, and arbitrary identification numbers assigned to individual graphic entities such as points, line segments and polygons.
It is important to note that nominal location identifiers do not prescribe the position of the entities in space unless cross-reference is made to another data set, typically a map, which does specifically define the location of each name or code number involved. Four types of location identifiers are used: a) Points - as abstractions of small phenomena or surrogates for larger phenomena, b) Line segments - for linear feature, c) Arbitrary regular area - grid cells, pixels, d) Irregular polygons - surface descriptive.
An entity or geographic feature that occupies a position in space about which data describing the attributes of the entity and its geographic location are recorded. It is a discrete generic class with basic connectedness and interdependence as a single data set, i.e., land use as a class has separate entities of residential, commercial, industrial, agricultural, etc. The class is a set of geographic entities derived from a common set of criteria, thus sharing spatial character and structure, e.g., ownership parcels, intersections, street segments, etc.
geographic hot links
A hypertext-like capability that allows for various kinds of data sets and software objects to be attached to geographic features and queried or initiated on request; e.g., pictures can be retrieved by pointing at features on the map, or more detailed views of data can be brought up in other windows by touching particular features in the active window. Hot links are a way to "drill down" into greater levels of detail by linking views at multiple scales in much the same way that hypertext links topics in related documents. Hot links can be used to launch more sophisticated applications by simply touching a feature on the map.
Computer system functional activity processing which involves spatial relationships such as: a) Engineering (e.g., streets and roads, sidewalks, traffic channeling, pedestrian and bicycle facilities, public facilities and capital improvements); b) Traffic (e.g., traffic flow, volumes, accidents and accident locations, street nomenclature, location); c) Refuse Collection (e.g., route, customer location, route distance, facilities); d) Census (e.g., voter registration, voter precincts, demographics, vital statistics, births and deaths); e) Planning and Community Development (e.g., parcel location and attributes, land use and zoning, development activity and intensity, growth pattern); f) Police (e.g., criminal offenses, police precincts, complaints, traffic accidents, arrest and arrest histories, crime patterns); g) Property Assessment (e.g., legal description, location of property, land and building assessments, improvements, sale history, physical characteristics of property); h) Utilities (e.g., service - power, water, sewer - history, facilities, routes, service networks, customer locations, complaints); i) Licenses (e.g., type - business and occupation, dog, bicycle - of license, location); j) Fire (e.g., fire incidents, station locations and districts, fire location histories, building locations and structural characteristics, arson patterns); k) Health and Human Services (e.g., public health services locations, vital statistics - births and deaths, visiting nurse routes and service locations, environmental health inspections).
GIS basic question types
A GIS can be distinguished by listing the types of questions it can (or should be able to) answer as opposed to being described: a) through formal definitions, and b) through its ability to carry out spatial operations, and linking data sets together with location as the common key. There are five generic questions that a sophisticated GIS can answer:
1 - Location What is at ...? The first of these questions seeks to find out what exists at a particular location described in various ways (e.g., place name, post or zip code, or geographic references).
2 - Situation/Condition Where does it exist? The second question is the converse of the first and requires spatial analysis to answer. Instead of identifying what exists at a given location, a location is found where certain conditions are satisfied (e.g., an unforested section of land of at least 2000 square meters in size, within 100 meters of a road, and with soils suitable for supporting buildings).
3 - Trends What has changed since...? The third question involves both of the first two, and seeks to find the differences within an area over time.
4 - Patterns What spatial patterns exist? The fourth question is more sophisticated; the question is asked to determine whether cancer is a major cause of death among residents near a nuclear power station or how many anomalies there are that don't fit a predetermined pattern and where they are located.
5 - Modeling What if...? The fifth question is posed to determine what happens, for example, if a new road is added to a network, or if a toxic substance seeps into the local groundwater supply. (Answering this type of question requires both geographic as well as other information, and possibly scientific laws.)
GIS cognitive science
Concerns how people think about their geographic surroundings and their spatial-temporal relationships. This knowledge is used to improve the design of GIS and computer mapping and the related technologies to improve the science and the environment.
GIS data model
A GIS structure providing a framework for data manipulation and display of map data for applications such as:
(a) location verification,
(b) location correlation,
(c) locational relationships,
(d) district coding,
(e) route analysis,
(f) area analysis and
(g) mapping/display creation.
GIS data used in the model can be raster, vector, textual and hybrid types from many diverse sources using state-of-the-art techniques: geometry from CAD systems; video and slide images; commercially available digital data (vector and/or raster); existing maps, charts, and drawings; original survey data (aerial, land, subsurface, oceanic, and GPS); aerial photos, orthophotos, and satellite imagery; existing digital records, files, database tables, and spreadsheets; hard copy documents, log books and files; surface terrain data (TIN and grid); etc.
The model when applied can be used to undertake and perform many applications including transportation, environmental and natural resource management, business application, government infrastructure, energy exploration and production, utilities, map and chart publishing, land information management, hydrography, planning and development.
GIS design alternatives
GIS systems rely on one of three basic overall systems design alternatives: 1) street span systems (consists of address range records in which the beginning and ending intersection points describe a street span), 2) street/line segment systems (consists of beginning and ending node points from which an interconnecting line segment is drawn, to which an address range and geocodes are attached), and 3) site address/polygon systems (consists of node points associated with line segments/arcs which define polygons, to which a site address and geocodes are attached).
GIS development strategy
To develop a GIS, an organized approach should be taken to obtain a successful system, and includes the following phases:
a) geographic information needs assessment (an analysis of operations that will determine exactly how the GIS should be designed in order for it to be fully utilized in everyday routines);
b) analyze existing systems and create detailed GIS design (an analysis to summarize varying aspects of how the GIS will operate including database design, software design, hardware design, application design, and personnel and management design);
c) implementation plan (provides a detailed program of steps for the development of the GIS including scheduling, management requirements, budget, equipment and personnel resources);
d) initiate implementation plan, prototype, create land base and install system (include system acquisition and installation, training users in GIS system software and the operating system, and prototype project to allow for modification based on testing under operational conditions);
e) data conversion of other records (the organization's records and hard copy maps including the land base are integrated into the GIS over an extended period of time); and
f) technical support (insures that the user has access to GIS professionals to resolve day-to-day hardware and software problems and questions).
GIS standards categories
communications (cabling, network protocols)
DATA COLLECTION AND TRANSFORMATION STANDARDS
geodetic control, locational accuracy, base map
mapping scale, resolution
data content, completeness
classification system, coding methodologies
digitizing-automation techniques (image
SPATIAL DATA PROCESSING STANDARDS
GIS software - functionality, data representations
data models, structures (i.e. topological,
data manipulations - (illegal overlays)
DATA PRESENTATION STANDARDS
cartographic design - map layout, legends, graphic quality
feature placement - annotation, completeness, accuracy
DATA MANAGEMENT STANDARDS
data access - dissemination policies, data archives
meta-data - documentation of quality,
file structure, index
DATA EXCHANGE/TRANSFER STANDARDS
format - exchangeable among diverse software and
hardware configurations (without losing
media - hard copy, tape, CD
data processing knowledge (computing, networks,
database management, programming)
resource expertise (i.e., land use planning,
wildlife ecology, transportation planning,
spatial data analysis knowledge
global positioning system
A satellite-based device that records x, y, z coordinates and other data. It is a system developed by the United States Department of Defense that is based on a constellation of satellites orbiting the Earth at very high altitudes. Abbreviated GPS. GPS receivers are inexpensive and small enough to be carried by anyone, anywhere, to determine their general or an exact x,y,z location on the Earth's surface and record data while driving, flying, or hiking. The ground locations are calculated by signals from the satellites orbiting the Earth. GPS is available for geodetic control surveying, for providing very precise position and velocity fixes at discrete points in time, and for GIS applications such as in-vehicle navigation systems. The GPS also allows 24-hour, all-weather operational capacity in both navigation and relative positioning. See GPS.
graphic map features
Map graphic features or elements can be classified as points, lines, areas, or "raster." In GIS, these features are grouped together to form more complex objects such as "networks" of streams or roads, three-dimensional terrain "surface," and multi-polygon regions. The first four of these feature types are:
1) Points - GIS map "points" have no length or area but simply define the coordinate location of the feature (survey monuments, wells, mountain peaks, building permits, and traffic incidents are represented as points in a GIS database).
2) Lines - Lines have a linear extent in the GIS database but no area. (Road centerlines, stream centerlines, sewer lines, and utility mains are represented as lines in a GIS database.)
3) Areas - Areas, normally called "polygons" or "regions," are defined by a set of enclosing perimeter lines and are two-dimensional (property parcels, census tracts, and soils are represented as areas in a GIS database).
4) Raster Data - "Raster" or "grid-based" format areas and other map features as cells of a grid matrix; the fineness of the grid or the size of the cells in the grid matrix determines how accurately original map features are represented (scanned images of documents and satellite imagery are examples of raster data).
See GIS glossary: h-t.