Vocabulary

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.