GIS

Geoid

Gravity-defined, mean-sea-level surface of the earth. Ocean water would settle if only gravity, winds and tides don’t exist.

Ellipsoid

Smooth, mathematical model of the earth. Used for lat/long coordinates.

Datum

Full coordinate system that tells where the ellipsoid settles on the earth’s system.

Intersect

Overlap only

Union

Keep all areas from both layers

Geographic Coordinate System

Uses lat and long to describe locations on the Earth’s surface. Exact location of tree.

Projected Coordinate System

Takes curved earth and projects it onto a flat surface. Meters/feet. Measuring tree spacing, etc.

Shapefile

Actual geospatial data stored as a collection of files. Older ESRI format. Geometry and attributes.

Feature Class

Collection of features that share the same geometry type such as points/lines/polygons. They have a common attribute scheme and the same spatial reference. Discrete, lives inside a geodatabase. More advanced capabilities like larger datasets, domains, topology. Most operational data to be stored in a geodatabase.

Hillshade

Grayscale 3d, terrain for slope and aspect. Sun’s position taken into account. Multidirectional combines light from multiple sources. Traditional using illumination from one direction using altitude and azimuth.

Feature

Single real-world object. Road, pole, etc. Stored in geodatabase.

Azimuth

Angle formed north relative to observer and celestial body.

Attribute

Info about feature. On a tree, species, age, height, etc.

Geometry

Shape and location of feature

Layer

Dataset displayed on the map. Roads, streams, boundaries. Turn them off and on independently.

Geodatabase

Centralized data repository that stores, queries, and manages spatial coordinates.

Field

Column in an attribute table. Pole ID, Material, Height

Symbology

Appearance. Color size etc.

Snapping

Pulls cursor to nearby features.

Metadata

Data about the data. Who created it, when, what coord system used.

Projection

Coordinate systems. Converts the Earth’s 3d surface into a flat, 2d cartesian plane (x, y axis)

Clip

Cuts one dataset into another AR roads —> Pulaski Roads

Dissolve

Combines neighboring polygons.

Geoprocessing

Any GIS tool that changes or analyzes data

Query

Search. Trees [taller than] 40 feet. Etc. Select by attributes.

Geographic Information System

System for storing, managing, analyzing, displaying data

Geometry and Attributes

Two main parts of GIS: _____ is lat long etc and ______ is what it is like species, height, etc.

Vector Data

Discrete (individual) objects. Tree, power line, road, etc. Point/Line/Polygon

Raster Data

Continuous or categorical. Stores the world as pixels. Each pixel stores one value. Temp, Elevation, Rainfall, Satellite Imagery, Land Cover, Slope.

Cardinality

Number of records that can relate to each other between two tables. How many things on one side can connect to how many things on the other side?

Query

Search. Select by attributes or select by geometry.

Join

Process that connects two data tables or map layers together. Adds attributes from one layer or table to another and requires a common field.

Inner Join

Intersection. Keeps records that have a match in both tables. “Don’t Keep All Target Features”

Outer Join (Left)

Preserve. Keeps all records from one table, even if there isn’t a match. Unmatched values are Null. “Keep All Target Features”. Unmatched records can reveal missing data or incomplete inspections.

LiDAR

Light Detection and Ranging

LiDAR works by

using laser imaging (ultraviolet or near-infrared source, pulse) which reflects (return). Measures how long it takes for pulse to return to the sensor. Variable distance of the objects. Sonar for sound, Radar using radio, Lidar uses light from laser.

Attribute Table

Spatial Join

Attribute Join

Topology

Importance to understand gaps, overlaps, disconnected lines. Topology helps maintain spatial integrity.

Buffer

Neutral or protected strip of land

Accuracy

How close a mapped point is to its actual location

Precision

How detailed and repeatable the measurements are

Georeferencing

Assigning real world location info (coordinates) to digital images, maps, data. Lat/Long etc.

Attribute domain

Rules that describe the available values of a field type

Map Projection

Way to depict the curved surface of the earth on a flat surface

Raster

Spatial data model that represents the world as a grid of equal sized cells or pixels.

Continuous

Raster data that changes across a landscape like DEM, rainfall, surface temps

Discrete

Categorical data where cells are grouped into classes such as land-cover types (forest etc) or soil classifications

Define Projection

Use when data has no defined coordinate system (Spatial reference). Changes metadata.

Project

Change the projected coordinate system to a different coordinate system.

XY Data to Point

Add CSV to project. File with locations from lat and long. Assign coordinate system.

Enterprise GIS

Many people work with the same centralized data

Domain

Set of rules that tells a database what values are allowed in a specific field. Such as allowed words, or range “min vs max number or data”

Datum

Mathematical model that defines the size and shape of the earth to anchor a coordinate system. The global is WGS84 North America is NAD83. It locks a shape in place relative to the Earth. Centers the ellipsoid at the earth’s exact center of mass. If two datasets use different datums they can appear offset to one another.

Definition Query

Filters which features are displayed in a layer without deleting or modifying the underlying data. You have 10,000 poles, you can display only the active poles without deleting anything else.

Geocoding

Turning written text into coordinates

Georeferencing

Aligning digital objects to real world coordinates

Scale

Ratio between distance on the map and distance on the real world ground