THE MARYLAND-NATIONAL CAPITAL PARK AND PLANNING COMMISSION
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Glossary of Planning and Geographic Information Systems (GIS) Terms Glossary of Planning and Geographic Information Systems (GIS) Terms

Glossary is usually defined as an alphabetical list of technical terms in some specialized field of knowledge. This knowledge base glossary provides a collection of knowledge base documents that define many technical terms. These terms are arranged alphabetically, but you can quickly jump to a specific term by selecting its first letter from the index of the knowledge base glossary below.

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Table
A set of data elements that has a horizontal dimension (rows) and a vertical dimension (columns) in a relational database system. A table has a specified number of columns but can have any number of rows.
Template
A coverage containing common feature boundaries, such as land-water boundaries, for use as a starting place in automating other coverages.
Theme
A user-defined perspective on a coverage, grid, tin or image geographic data set specified, if applicable, by a coverage name and feature class or data set name, attributes of interest, a data classification scheme, and theme-specific symbology for drawing.
Tic
Registration or geographic control points for a coverage representing known locations on the Earth's surface. Tics allow all coverage features to be recorded in a common coordinate system (e.g., Universal Transverse Mercator [UTM] meters or State Plane feet). Tics are used to register map sheets when they are mounted on a digitizer and to transform the coordinates of a coverage (e.g., from digitizer units [inches] to UTM meters).
Tile
The spatial unit by which geographic data is organized, subdivided, and stored in a map library. Tiles subdivide the area covered by a map library and organize the library data by location (e.g., counties might be the tiles in a statewide database). A tile can be a regular, geometric shape (e.g., a map sheet), or an irregular shape, such as a county boundary.
Topology
The spatial relationships between connecting or adjacent coverage features (e.g., arcs, nodes, polygons, and points). For example, the topology of an arc includes its from- and to-nodes, and its left and right polygons. Topological relationships are built from simple elements into complex elements: points (simplest elements), arcs (sets of connected points), areas (sets of connected arcs), and routes (sets of sections, which are arcs or portions of arcs). Redundant data (coordinates) are eliminated because an arc may represent a linear feature, part of the boundary of an area feature, or both. Topology is useful in GIS because many spatial modeling operations don't require coordinates, only topological information. For example, to find an optimal path between two points requires a list of the arcs that connect to each other and the cost to traverse each arc in each direction. Coordinates are only needed for drawing the path after it is calculated.
Trade-Off
A balancing or exchange of factors or conditions, not all of which are attainable. Trade-offs are used in decision-making situations when complete satisfaction is not possible. Trade-offs involve sacrifice of one good for attainment of another.
Traffic Levels Of Service (Los)
See LEVELS OF SERVICE. a. A set of operating conditions describing the ability of a road network to handle traffic. Level A specifies the best traffic conditions; Level F indicates gridlock. b. The adequacy of the road and street network in the county transportation system is generally measured and expressed in terms of its LOS. Each level of service is one in a hierarchy of indices that evaluate the level and severity of automotive traffic congestion on a specific road segment or at specific intersections. The General Plan recommends the minimum acceptable LOS by Tier.
Transfer Of Development Rights (Tdr)
A growth management tool used to protect designated rural and environmentally sensitive areas by allowing development rights to be transferred to properties in other parts of the county.
Transit District Overlay Zone (Tdoz)
A mapped zone superimposed over other zones in a designated area around a Metro station. The TDOZ may modify certain requirements for development within those underlying zones. Permitted uses of the underlying zones are unaffected. However, underlying zones can be changed via the TDOZ.
Transit Master Plan (Tmp)
A five-year comprehensive blueprint for regional and local bus and paratransit service to be provided in and by Prince George's County, prepared by the Department of Public Works and Transportation.
Transit Supporting Development (Tsd)
Similar to TOD, transit-supporting development is land use that is generally sited and designed to increase, as opposed to maximize, transit ridership.
Transit-Oriented Development (Tod)
Land uses that are sited, designed and combined to maximize transit, particularly rail, ridership.
Transportation Demand Management (Tdm)/Transportation System Management (Tsm)
Techniques used to increase the efficiency of the existing transportation system through lower cost programs like ride sharing, bus fare subsidy, parking management, and flextime.
Transportation Improvement Program (Tip)
A six-year regional schedule for the study, acquisition, upgrading, or development of major highway, transit, bike and pedestrian facilities, and services. A joint effort of the National Capital Transportation Planning Board and its constituent jurisdictions - principally the state transportation agencies of Maryland, the District of Columbia, and Virginia¬óthe TIP complements the CLRP (see above). Any project that is to be a candidate for federal financial assistance must be included in both plans.
Tree Conservation Plan
A site map that delineates tree save areas and text that details the requirements, penalties or mitigation negotiated during the development and/or permit review process.