GPS, Coordinate Systems, Projections & Feature Creation Flashcards
The basics of creating features in GIS
Georeferencing
Aligning Geographic data to a Coordinate System.
May involve shifting, rotating, scaling, skewing, warping, rubbersheeting or orthorectifying.
Projections
The method by which the curved surface of the earth is portrayed on a flat surface
Geocoding
Converting street addresses into spatial data, usually referencing address information from a street segment layer.
Reverse Geocoding
Finding a street address from a point on the map.
Orthorectification
The process of correcting the geometry of an image so that it appears as though each pixel were acquired from directly overhead. Uses elevation data to correct terrain distortion in aerial or satellite imagery.
Heads-up Digitizing
Manual digitization by tracing over a feature.
Datum
A system of coordinate positions on a surface. A geodetic datum is the basis for calculating positions on, above, or below the earth’s surface.
Precision
Closeness of a repeated set of observations to each other.
Accuracy
Closeness to true position.
Sliver polygon
A small, narrow polygon that appears along the borders of polygons following the overlay of two polygons. May indicate topology problems.
Union
All features that exist in either set are retained.
Intersect
All features that overlap are retained.
Address Locator
Defines the process for geocoding.
Transformation
Converting the coordinates from one system to another.
Geographic Coordinate System
Lat/Long. Uses a datum, prime meridian, and angular unit of measure (degrees, minutes, seconds).
Projected Coordinate System
Uses a linear system of x,y,z. Relies on a Geographic Coordinate System, Map Projection, and linear units of measure.
Decimal Degrees
Values of lat & long expressed in decimal format.
Image Processing
Changing the values of an image for analysis or enhanced display.
Density Slicing
Highlight areas that appear to be uniform in tone but aren’t. Often used for remote sensing of vegetation.
Low/High Pass Filtering
Spatial filter that blocks high or low frequency radiation, resulting in a smoother or sharper image.
Edge Enhancement
Emphasize the appearance of edges & lines
