Geographic Information Systems (GIS) Vocab 2

Discrete object view

World is conceptualized and visualized as a series of separate objects with fixed boundaries/points

Continuous field view

World consists of continuously varying fields with less defined boundaries

Nominal attribute data

No way to order data aside from unique identifiers, e.g. business name, land type

Ordinal attribute data 

Can be ranked from, for example, “highest to lowest”, but nothing else; e.g. road type (good, fair, poor)

Interval attribute data

Numerical differences are significant, but no true zero point, e.g. temperature in Fahrenheit

Ratio attribute data

Numerical differences are significant, with fixed zero point, e.g. elevation above sea level

Attribute tables

Made up of records (particular things) and fields (characteristics of those things)

File geodatabase 

A folder that contains a collection of files. It is used to store, query, and manage geospatial and attribute data

Feature class

A single layer in GIS

Feature dataset

A grouping of feature classes (which usually share a coordinate system)

Metadata

The descriptive/background information provided about a dataset

Spatial analysis 

The process of examining the spatial characteristics of data or how objects relate to each other across distances 

Queries

Asking the database about attributes; a category of spatial analysis

Measurements

Calculating distance, area, etc.; a category of spatial analysis

Transformations

Calculating new data; converting raster to vector and vice versa; a category of spatial analysis

Descriptive summaries 

Analysis which describes trends in the data; a category of spatial analysis

Optimization

Mathematical, computational methods to solve geographic problems; a category of spatial analysis

Hypothesis testing

Analysis to see if predicted patterns are actually there; a category of spatial analysis

SQL (Structured Query Language)

The program used by ArcGIS Pro to conduct simple and complex queries

AND operator 

Intersect; selects features which meet two (or more) criteria 

OR operator

Union; selects features which meet at least one of two criteria

NOT operator

Negation; omits features which meet a certain criteria

XOR operator

Exclusive or; selects features which meet one or another criteria, but not features that meet both

Relational operators 

Include = (equal to), <> (not equal to), < (less than), > (greater than), <= (less than or equal to), => (equal to or greater than) 

Simple queries

Searching for features which meet one criteria

Compound queries

Specifying multiple criteria

Spatial queries

A form of spatial analysis which selects records of objects based on their spatial relationships to others

Buffers 

A form of spatial query which creates a polygon of a certain specified distance around another point, line, or polygon 

Dissolve

A common spatial query where you create a new layer consisting of polygons you combined based upon some common criteria

Overlay

A type of spatial query that combines features from two or more layers to create a new layer

Intersect

A type of overlay that retains where the two (or more) features overlap

Identity

A type of overlay that retains all features from the first layer along with features in common from a second layer

Symmetrical difference 

A type of overlay that retains all features from both layers except for the features they have in common 

Union

A type of overlay that retains all features

Layout

How map elements are assembled in a GIS program

Visual hierarchy

How features are displayed on a map to emphasize their level of prominence

Reference maps

Maps that primarily show the locations of features

Thematic maps 

Maps that focus on a particular subject or theme and prioritize data display over geographic features

Chloropleth maps

A type of thematic map where data is displayed according to a data classification system 

Graduated symbol maps

A type of thematic map where different-sized symbols are used to convey thematic information

Natural breaks (Jenks) 

A type of data classification that involves selecting class break levels by searching for spaces in the data values 

Quantiles

A type of data classification that involves attempting to place an equal number of data values in each class

Equal intervals 

A type of data classification that involves selecting class break levels by dividing the total span of values (from highest to lowest) by the number of desired classes 

Standard deviation

A type of data classification that involves computing class break values by using the mean of the data values and the average distance of the value from the mean

RGB (red-green-blue)

The color scheme that is used for many digital formats

CMYK (cyan-magenta-yellow-black)

The color scheme that is used for many printed formats

JPEG (“Joint Photographic Experts Group”)

This type of file tends to have degraded quality but is space-efficient 

TIFF (“Tagged Image File Format”)

This type of file tends to be higher-quality but is generally larger

Global Positioning System (GPS)

Specifically called NAVSTAR [ ], is a satellite-based radio-navigating system that provides 3D location and navigating information to users anywhere on Earth

Space segment

The segment of GPS that consists of the satellites in orbit and the signals they broadcast

Control segment

The segment of GPS that consists of the infrastructure on the ground that communicates with the satellites

User segment 

The segment of GPS that refers to the device that is being used to request GPS coordinates 

Satellite signal distance equation

Distance = elapsed time x speed of light

L1 (coarse acquisition code)

The signal that is publicly available and is the main code used for civilian purposes

P-code

Encrypted by the Y-code, is a military-grade signal that is more accurate than L1, not accessible through civilian GPS receivers

Ephemeris 

Data about a GPS satellite’s position in orbit 

Trilateration

Finding a location in relation to three points of reference; used to estimate latitude, longitude, and elevation

Autonomous GPS 

GPS readings that haven’t been corrected

User Equivalent Range Error (UERE)

The total effect of GPS error

Clock error

Difference between the clock on a satellite and time at the ground station

Ionospheric error

The main source of autonomous GPS error, is caused by free electrons in the upper atmosphere, which bend and delay signals

Ephemeris error

GPS error caused by a satellite broadcasting incorrect information about its location and orientation due to a difference between actual and predicted location

Tropospheric error 

GPS error caused by climate conditions (temperature, pressure, humidity), an issue for satellites at low orbital angles

Receiver noise

GPS error caused by bad quality of the receiver and any line of sight problems due to a “hostile” GPS environment

Multi-path error

When a GPS signal bounces off another object, causing signal delay and therefore, an inaccurate reading

Dilution of precision (DOP)

A geometric issue that occurs when satellites are close together in their orbits 

Differential GPS (DGPS)

Involves computing a GPS-computed position at a location called a base station by using the actual surveyed location of the base station

Continuously Operating Reference System (CORS) network

A DGPS source that was developed by the National Geodetic Survey and has over 1,800 base stations in US territory

Wide Area Augmentation System 

A DGPS source that works with satellites to broadcast real-time corrections; run by the Federal Aviation Administration (FAA) to aid in aircraft navigation across the US, Mexico, and Canada

Recreational grade

GPS equipment that is for everyday use, not especially precise as correction options are limited (no DGPS), is very affordable (under $200)

GIS-grade

GPS equipment that is designed for mapping professionals; often has sub-meter accuracy with many correction options (DGPS); moderately expensive (several hundred dollars); often paired with an antenna and/or base station

Survey-grade

GPS equipment that is used for engineering, construction, and surveying purposes where preciseness is critical; uses different standards of data collection; can have sub-centimeter accuracy, many correspond with a network of base stations