P-GIS Glossary,

Posted on Jul 2, 2007 By : Mizake Laziaf
This glossary is a sub-set of one developed by the Urban and Regional Information
Systems Association (URISA)


Pan
This term is usually used in the phrase “pan and zoom” and refers to elements of a computer interface that enable use of a mouse cursor on a computer screen to “click and drag” your viewing area so that an adjacent area is displayed.


Parcel
A portion of the earth defined by a boundary inside of which certain assigned rights apply regarding occupancy and/or use of land, air or water apply. Can also include linked attributes that define the rules and conditions for exercising these rights.

Photogrammetry
This term is used in surveying and mapping, and refers to the science, art and technology of obtaining reliable measurements and maps from photographs. This is also, the means for measuring or plotting planimetric, topographic, and other features of the earth through the use of aerial photographs and ground control.

Pixel
This acronym stands for Picture Element, the smallest non-divisible image-forming unit of a plot or video display. Each cell can have assigned attributes, in addition to color. In raster processing, pixels refer to a single cell within a matrix of grid cells. See Image.

Planimetric Map
Horizontal depiction of map features on a two-dimensional plane without any reference to contours or topographic relief. Typical features defined within a planimetric map include such natural and cultural features as streams, roads, shorelines, waterways, building footprints, reservoirs, bridges, roadways, overpasses, sidewalks and parking lots.

Point
A point is a single X,Y (optionally Z) location in space. It is a dimensionless geometric feature having no other spatial properties except location. Many different natural and man-made features are modeled as points in spatial databases including trees, fire hydrants, poles, building, etc.

Point-In-Polygon
A spatial query that determines which polygon boundary encompasses a specified point. A typical operation is to select multiple points within a boundary and assign to them an attribute equal to a characteristic assigned to all areas within the boundary (i.e. soil type) to the attributes describing the point. As a variation, one or more polygons are selected and all points within them are likewise assigned new attributes. Process can be extended to apply to linear features (line-in-polygon) and closed polygons (polygon-in-polygon) located within or partially within polygons as well.

Polygon
  • Closed plane figure bounded by three or more line segments with a nonzero area. Alternatively, a polygon is a multisided feature that represents an area on a map. Many different natural and man-made features are typically represented by polygons in a spatial database including zoning districts, soil types, water bodies, building footprints, lot boundaries, etc.
  • A type spatial query wherein the spatial selection area is a polygon shape rather than a square, rectangle, or circle.

Polygon Overlay
  • A group of polygons on one or more layers, representing various areas that make up a particular geographic theme (e.g., soil types, zoning designations, parcels, land use, etc.)
  • Spatial analysis function that uses Boolean logic to combine two sets of polygon boundaries to create a third that represents an intersection or union of the first two.

Precision
In general, precision refers to how close a measured value matches another measured value.
  1. Degree of exactness with which a quantity is stated (i.e., the number of significant decimal places in an expressed coordinate value).
  2. Can be expressed in terms of "repeatability" of a measurement, i.e., the likelihood of deriving the same coordinate values from the same mathmatical calculations.
  3. In spatial databses, refers to how many places allocated to the storage of coordinate information.


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