6.5 Summary
Vocabulary
6.1: Vector Data Models
Append
Combines the spatial extent of two or more layers to create a new output polygon.
Arcs
Similar to the function of a line, but are curved.
Area Definition
An arc that connects to surround an area defining a polygon.
Buffering
The process of creating an output polygon layer containing a zone (or zones) of a specified width around an input point, line, or polygon feature.
Clip
A method that is used to extract features from an input point, line, or polygon layer that falls within the spatial extent of the clip layer.
Cluster Tolerance
A feature in GIS software that forces nearby lines to be snapped together if they fall within a user-specified distance.
Connectivity
The arc-node topology for the feature dataset.
Constant Width Buffers
This process will require users to input a value by which features are buffered.
Contiguity
Polygons that share an arc are deemed adjacent. The side of each arc can be defined.
Dissolve
Combines adjacent polygon features in a single feature dataset based on a single predetermined attribute.
Doughnut Buffer
A buffer that excludes the input polygon area.
Erase
Essentially the opposite of a clip. Whereas the clip tool preserves areas within an input layer, the erase tool preserves only those areas outside the extent of the analogous erase layer.
Error Propagation
Occurs when inaccuracies are present in the original input and overlay layers and are propagated through to the output layer.
Geoprocessing
Specialized software tools used to compare, analyze, or manipulate map layers and their underlying geographic data to create new sets of data.
Identity
Also referred to as “minus”, this overlay method creates an output layer with the spatial extent of the input layer, but includes attribute information from the overlay.
Intersection
This method employs the AND operator.
Line-on-Line Overlay
An operation that requires line features for both the input and overlay layer.
Line-in-Polygon Overlay
Similar to the point-in-polygon overlay, with that obvious exception that a line input layer is used instead of a point input layer.
Lines
Features composed of multiple, explicitly connected points.
Merge
Combines features within a layer into a single feature with identical attribute information.
Multiple Ring Buffers
A buffer field that changes width.
Node
A common coordinate pair between intersecting lines or polygons.
Overlay
To lie on top of another.
Point-in-Polygon Overlay
This operation requires a point input layer and a polygon overlay layer. A new output point layer is returned that includes all the points that occur within the spatial extent of the overlay.
Points
Zero-dimensional objects that contain only a single coordinate pair.
Polygon-in-Polygon Overlay
This operation employs a polygon input and a polygon overlay.
Polygon-on-Line Overlay
The opposite of the line-in-polygon operation. In this case, the polygon layer is the input, while the line layer is the overlay.
Polygon-on-Point Overlay
The polygon layer is the input, while the point layer is the overlay.
Polygons
Shapes created by multiple lines that loop back to create a “closed” feature.
Select
An output layer based on the selection of a particular feature(s) from the input layer.
Setback Buffers
Buffer that includes ONLY the input polygon area.
Sliver
A common error produced when two slightly misaligned vector layers are overlain.
Spaghetti Data Model
A model in which each point is represented as a string of coordinate pairs with no inherent structure.
Spatial Join
A hybrid between an attribute operation and a vector overlay operation. It results in the combination of two feature dataset tables by a common attribute field.
Split
An operation that is used to divide an input layer into two or more layers based on a split layer.
Symmetrical Difference
Employs the XOR operator, which results in the opposite output as an intersection.
Topological Data Model
A model that is characterized by the inclusion of topological information within the dataset.
Topology
Rules that model the relationships between neighboring points or polygons, and determines how they share geometry.
Union
Preserves all features, attribute information, and spatial extents from both input layers.
Variable Width Buffers
A premade buffer field within the attribute table to determine the buffer width for each specific feature in the dataset.
Vertex
Each bend along a line or polygon that is not the point of intersect.
6.2 Raster Data Models
Aspect Maps
Uses slope information to produce output raster images whereby the value of each cell denotes the direction it faces.
Boolean Raster Overlay
Connectors AND, OR, and XOR can be employed to combine the information of two overlying input raster datasets into a single output raster.
Cell-by-Cell Caster Encoding
Encodes a raster by creating records for each cell value by row and column.
Global Operations
Determining basic statistical values for the raster as a whole.
Interpolation
Technique that estimates the value of all unknown points between the known points.
Kriging
A complex geostatistical technique that employs semivariograms to interpolate the values of an input point layer and is more akin to a regression analysis.
Local Operations
A raster output dataset where the output value at each location is a function of the value associated with that location.
Mathematical Raster Overlay
The numbers within the aligned cells of the input grids can undergo any user-specified mathematical transformation.
Neighborhood Operations
Neighborhood operations examine the relationship of an object with similar surrounding objects.
Positive Spatial Autocorrelation
Nearby values of a variable that tend to be similar.
Quad-Tree Raster Encoding
This method divides a raster into a hierarchy of quadrants that are subdivided based on similarly valued pixels.
Relational Raster Overlay
This method utilizes relational operators to evaluate conditions of the input raster datasets.
Run-Length Raster Encoding
This method encodes cell values in runs of similarly valued pixels and can result in a highly compressed image file.
Slope Maps
Are made to assess watershed units, inventory forest resources, determine habitat suitability, estimate slope erosion potential, and so forth.
Spatial Resolution
The number of pixels utilized in construction of a digital image.
Surface
Dataset that contains an attribute value for every locale throughout its extent.
Target Cell
Cell found in the center of the 3-by-3 moving window.
Terrain (Elevation) Analysis
When information is calculated on raster surfaces such as DEMs.
Viewshed Analysis
Technique that uses the elevation value of cells in a DEM or TIN to determine those areas that can be seen from one or more specific location.
Watershed Analyses
A series of surface analysis techniques that define the topographic divides that drain surface water for stream networks.
6.3: Satellite Imagery and Aerial Photography
Active Satellites
Satellites that detect signals from artificially generated energy sources, then strengthens and emits the signal to its next destination.
Geostationary Satellites
Satellites that circle the earth proximal to the equator once each day.
Orthophotos
A vertical photographs that have been geometrically “corrected” to remove the curvature and terrain-induced error from images.
Passive Satellites
Reflects the signal from one earth station to other earth station(or stations) without any amplification or retransmission.
Radiometric Resolution
Refers to the sensitivity of the sensor to variations in brightness and specifically denotes the number of grayscale levels that can be imaged by the sensor.
Spatial Resolution
The number of pixels utilized in construction of a digital image.
Spectral Resolution
Denotes the ability of the sensor to resolve wavelength intervals, also called bands, within the electromagnetic spectrum.
Sun-Synchronous Satellites
A satellite that can synchronize to a near-polar orbit of the sensor with the sun’s illumination.
Temporal Resolution
The amount of time between each image collection period and is determined by the repeat cycle of the satellite’s orbit.