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Data Models - Data Exploration: A data-centered query and analysis process to explore and understand data. - Dynamic Segmentations: A data model that employs linearly measured data on a coordinate system for
analysis. - Georelational Data Model: A vector data model that ...
- Data Exploration: A data-centered query and analysis process to explore and understand data.
- Dynamic Segmentations: A data model that employs linearly measured data on a coordinate system for
analysis.
- Georelational Data Model: A vector data model that uses a split system to store geometries and their
attributes separately.
- GeoSpatial Data: Data describing both the locations and characteristics of spatial features on the
Earth's surface.
- Object-Based Data Model: A data model using objects to organize spatial data, storing geometries and
attributes in a unified system.
- Raster Data Model: A data model represented by a grid of cells, capturing the spatial variation of
features.
- Relational Database: A collection of tables interconnected by keys, enabling data storage and retrieval.
- Vector Data Model: A spatial data model using points and their x,y coordinates to construct spatial
features like points, lines, and polygons.
Topology and Spatial Relationships
- Topology: A subfield of mathematics applied in GIS to ensure spatial relationships between features
are expressed explicitly.
- Triangulated Irregular Network (TIN): Composite vector data approximating terrain with non-
overlapping triangles.
Map Projections
- Azimuthal Projection: A map projection that retains accurate directions, using a plane as the projection
surface.
- Central Lines: Refer to the central parallel and central meridian that define the origin of a map
projection.
- Clarke 1866: A ground-measured ellipsoid that is the basis for the North American Datum of 1927
(NAD27).
- Conformal Projection: A type of map projection preserving local shapes.
- Conic Projection: A type of map projection that uses a cone as the projection surface.
,- Cylindrical Projection: A type of map projection that employs a cylinder as the projection surface.
- Datum: The basis for calculating geographic coordinates, requiring an ellipsoid for its derivation.
- Datum Shift: A change from one datum to another (e.g., from NAD27 to NAD83), potentially leading to
significant horizontal shifts in point positions.
- Equidistant Projection: A type of projection that maintains correct relative area sizes.
- Lambert Conformal Conic Projection: A widely used map projection serving as the basis for State Plane
Coordinate (SPC) systems in many states.
Coordinate Systems and Measurement
- Decimal Degrees (DD) System: A measurement system for latitude and longitude values represented as
decimal numbers (e.g., 42.5).
- Degrees Minutes Seconds: A coordinate measurement system for latitude and longitude values
represented in degrees, minutes, and seconds format (e.g., 42 30' 00").
- Ellipsoid: A model that approximates the Earth's shape, also referred to as a spheroid.
- False Easting: A value applied to the origin of a coordinate system to adjust x-coordinate readings.
- False Northing: A value applied to the origin of a coordinate system to modify y-coordinate readings.
- Geographic Coordinate Database (GCDB): A database developed by the US Bureau of Land
Management (BLM) containing latitude and longitude values, with additional descriptive information for
section corners and monuments recorded in the Public Land Survey System (PLSS).
- Geographic Coordinate System: A location reference system for spatial features on the Earth's surface.
- GRS80: A satellite-determined ellipsoid used in the Geodetic Reference System.
Latitude ✔️The angle north or south of the equatorial plane
Longitude ✔️The angle east or west from the prime meridian
Map Projection ✔️A systematic arrangement of parallels and meridians on a plane surface
Meridians ✔️Lines of longitude that measure locations in the E-W direction on the geographic
coordinate system
, NAD27 ✔️North American Datum of 1927 which is based on the clarke 1866 ellipsoid
NAD83 ✔️North American Datum of 1983 which is based on the GRS80 ellipsoid and has its origin at
the center of the ellipsoid
Parallels ✔️Lines of latitude that measure locations in the N-S direction on the geographic coordinate
system
Principal scale ✔️Same as the scale of the reference globe
Projected coordinate system ✔️A plane coordinate system that is based on a map projection
Projection ✔️The system used to transfer locations from Earth's surface to a flat map.
Public Land Survey System (PLSS) ✔️A land partitioning system used in the United States
Reference globe ✔️A reduced model of the earth from which map projections are made. Also called a
nominal or generating globe
Reprojection ✔️Projection of spatial data from one projected coordinate system to another
Scale factor ✔️Ratio of the local scale to the scale of the reference globe. The scale factor is 1.0 along a
standard line.
Spheroid ✔️A model that approximates the earth. Also called ellipsoid
Standard line ✔️Line of tangency between the projection surface and the reference globe A standard
line has no projection distortion and has the same scale as that of the reference globe
Standard meridian ✔️A standard line that follows a meridian
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