ENGRG 59910 GIS Final Review

Flashcards for vocabulary review of key GIS concepts.

Geographic Information System (GIS)

Links locational (spatial) and database (tabular) information and enables a person to visualize patterns, relationships, and trends.

Hardware (GIS Component)

The computer and peripherals on which the GIS operates.

Software (GIS Component)

Provides the functions and tools users need to store, analyze, and display geographical information.

Data (GIS Component)

A crucial GIS component that must be accurate, including vector, raster, image, and attribute types.

People (GIS Component)

Essential for managing the GIS system and developing plans for its application.

Methods (GIS Component)

Well-designed plans and application-specific business rules describing how technology is applied.

Vector Data Model

Spatial information is modeled using points, lines, and areas.

Raster Data Model

Space is divided into a regularly spaced grid, with each cell coded according to what is on the surface.

Point (node) - Vector Data Model

0-dimension, single x,y coordinate pair, zero area, tree, oil well, label location.

Line (arc) - Vector Data Model

1-dimension, two (or more) connected x,y coordinates, road, stream.

Polygon - Vector Data Model

2-dimensions, four or more ordered and connected x,y coordinates, first and last x,y pairs are the same, encloses an area, census tracts, county, lake.

Spaghetti Model (non-topological)

Lines and points are entered and may be visible, but the program does not recognize the relationships between lines. Each line is represented as a separate feature with a start node and an end node, possibly vertices in between.

Topological Vector Data Model

The connections and relationships between objects are described independently of their coordinates.

Polygon Topology Table

Links composing all the polygons.

Node Topology Table

List of the links that meet at each node.

Link (or line segment) Topology Table

List of the beginning and end nodes for each link; polygons to the right and left to the link

Resolution (GIS)

The minimum linear dimension of the smallest unit of geographic space for which data are recorded.

High Resolution (Raster)

Refers to raster with small cell dimensions; means lots of detail, lots of cells, large rasters, small cells.

Rasterization

Loses topological features; no information about relationships; positional accuracy decreases; depends on cell size.

Vectorization

Feature boundaries become jagged in the vector representation; topology is created (relationships).

Spheroid (Ellipsoid of Revolution)

A quadric surface obtained by rotating an ellipse about one of its principal axes.

Ellipsoid Definition

A mathematical model of the earth must be selected.

Geoid

A surface of constant gravitational potential.

Geodetic Datum/System

A coordinate system, and a set of reference points, used to locate places on the Earth (or similar objects).

WGS84 (World Geodetic System - 1984)

The datum on which GPS coordinates are based and probably the most common datum for GIS data sets with global extent. (Developed by DoD).

Shape (Conformal) Map Projection

A map projection which preserves shape, feature outlines look the same on the map as they do on the earth.

Area (Equal-Area) Map Projection

A map projection which preserves area, size of a feature on a map is the same relative to its size on the earth.

Distance (Equidistant) Map Projection

A map which preserves true scale for all straight lines passing through a single, specified point

Direction/Azimuth (Azimuthal) Map Projection

A projection which preserves direction for all straight lines passing through a single, specified point.

Conformality - Map Projection

Angles on the map are the same as they would be on a globe

Equivalence - Map Projection

Any unit area drawn on the map represents the same unit area on a globe

Distance - Map Projection

Straight line lengths on the map are the same as on a globe

Direction - Map Projection

Preserves the correct angle and distance in relation to the map center

Universal Transverse Mercator (UTM) Coordinate System

Underlying projection: Transverse Mercator. World divided into 60 six-degree-wide zones.

State Plane Coordinate System

Underlying projections: Lambert Conformal Conic for “east-west” areas; Transverse Mercator for “north-south” areas.

Control Points (GIS)

Identifiable entities with known coordinates.

Affine (Linear) Transformation

Scale, skew, rotate, translate, correct without distorting map far from GCPs. Cannot correct complex distortions.

Primary Key (Database)

Uniqueness, eliminate Redundancy.

Foreign Key (Database)

Linking tables, establishes relationships between tables.

Geodatabase

A physical store of geographic information (spatial, attribute, metadata, and relationships) inside a relational database management system (RDBMS).

Point Queries (Spatial)

what is at a particular location?

Range Queries (Spatial)

what is in a particular area?

Nearest Neighbor Queries (Spatial)

where is the nearest object to a particular location?

Spatial Join Queries

For each bus stop, find all restaurants within 100 feet (associate a bus stop with a restaurant based on spatial proximity).

Spatial Aggregate Queries

count the numbers of bus stops in community districts.

Classification and Reclassification

Attribute operation in which the attribute values change without altering the geometry.

Dissolve GeoProcessing Tool

Aggregates features based on specified attributes.

Merge GeoProcessing Tool

Append together layers of adjoining areas

Clip GeoProcessing Tool

Extracting an area of interest

Intersect GeoProcessing Tool

Combine attributes of intersected features

Union GeoProcessing Tool

Combine features and keep attributes of both

Buffer (GIS)

Creates one or more polygons of a prescribed extent around points, lines, or areas; defines spatial proximity.

Map Algebra

Cell by cell combination of raster layers using mathematical operations.

Raster Overlay

Combines attributes from two or more layers; often restricted to nominal (categorical) data; can be implemented using raster addition.

Local Raster Operations

Operate on individual cells, one-at-a-time, relative to the ones directly “below.”

Focal Operations

Assign data value to a cell based on its neighborhood (various definitions).

Zonal Raster Operations

operate based on defined regions, or zones, within an area

Raster-based Digital Elevation Model (DEM) / Digital Terrain Model (DTM)

Regularly spaced set of elevation points (z-values) .

Vector based Triangulated Irregular Networks (TIN)

Irregular triangles with elevations at the three corners.

Vector-based contour lines

Lines joining points of equal elevation, at a specified interval.

Point Clouds

Set of regular or irregularly spaced points with heights/distances e.g., LIDAR.

Slope (Terrain Analysis)

The inclination of the terrain; calculated as percentage or degrees.

Aspect (Terrain Analysis)

Direction that a surface faces; typically reported as an azimuthal angle (measured in degrees from the north clockwise).

Local Interpolation Method

Uses sample of known points to estimate an unknown value.

Global Interpolation Method

Uses every known point available to estimate an unknown value.

Exact Interpolation

Predicts a value at the point location that is the same as its known value; generates a surface that passes through the control points.

Inexact Interpolation (Approximate Interpolation)

Predicts a value at the point location that may differ from its known value.

Deterministic Interpolation Method

Provides no assessment of errors with predicted values.

Stochastic Interpolation Method

Offers assessment of prediction errors with estimated variances.

Gradual Interpolation Methods

Produce smooth surface between data points appropriate for interpolating data of low local variability

Abrupt Interpolation Methods

Produce surfaces with a stepped appearance appropriate for interpolating data of high local variability or data with discontinuities

Nearest Neighbor Interpolation (Thiessen polygons)

Value assigned from nearest sample

Inverse-Distance Weighting (IDW)

Value calculated directly from three (usually) nearest samples. Near one sample point, its influence greatly predominates. Must know!

Global Positioning System (GPS)

Satellite navigational system that provides accurate coordinates worldwide.

GPS Working Equation

Distance = Speed * Time

Multi-Path Error (GPS)

Occurs when GPS signals are reflected and the receiver detects two signal instead of one at different times