GIS Terms
Overlay Analysis
A GIS operation that combines multiple spatial datasets to create a new dataset. It is used to find common features, identify areas of convergence or divergence, and perform various spatial analyses.
Relational Database
A collection of tables that are logically associated to each other by at least one shared attribute (the key).
SQL (Structured Query Language)
A computer language that can be used to query (select) attribute data in a database. In ArcGIS Pro it is the underlying language of 'select by attribute.'
Points
A coordinate x,y pair that represents a location. Examples at different scales are power poles, water wells, and cities.
Boolean
A data type that can have one of two values, typically true or false. In GIS, Boolean expressions are used in queries to filter and select data based on conditions.
Geodatabase
A database designed to store, query, edit, and manage feature classes, raster data, tables, and annotations for a project.
Append
A geoprocessing operation that combines the features and attributes of one dataset with another dataset. It adds the records from one dataset to another.
Summarize Within
A geoprocessing tool that aggregates data from one dataset based on the spatial relationships with features in another dataset. It provides summary statistics for features within specified boundaries.
Buffer
A geoprocessing tool that creates a new polygon feature class around the features in the input feature class. It can operate on points, lines, or polygons.
Near
A geoprocessing tool that identifies the nearest feature in one dataset to each feature in another dataset. It calculates distances and reports the closest features.
Erase
A geoprocessing tool that removes a piece of one dataset using an overlying feature class. The output is a new feature class. Input and overlay features can be points, lines, or polygons.
Clip
A geoprocessing tool used to cut out a piece of one dataset using features in an overlapping dataset as a cookie cutter. The output is a new feature class. The 'cookie cutter' feature class is always a polygon; the other can be point, line, or polygon.
Pixel
A grid cell in a raster data set. The smaller the cell size, the better the resolution.
Reference Grid
A grid dividing a map equally where every row and column is labeled, it gives every square a unique identifier. For example, a map of Idaho might have a grid labeled A, B, C, D, and so on from west to east and 1, 2, 3, 4, and so on from north to south and Rexburg might be located in the grid box labeled G10.
Raster Data Model
A grid of square or rectangular cells used to represent real-world spatial data. Each cell has a numeric value which can represent varied features including building locations, elevation, and concentration of a pollutant.
Graticule
A grid on a map typically made of lines of latitude and longitude.
Dynamic Map
A map that can be interactively manipulated or changed by the user, often in real-time, to display different aspects or layers of spatial data.
Thematic Map
A map that focuses on a specific theme or topic, such as population density, land use, or rainfall distribution. It represents spatial data related to that theme.
Small scale map
A map that has less detail and typically covers a greater area. A typical example is a map of scale 1:1,000,000
Large scale map
A map that has more detail and typically covers a smaller area. A typical example is a map of scale 1:5,000.
Reference Map
A map that provides general information about geographic features and locations, such as roads, cities, and natural features. It serves as a background map for other thematic data.
Longitude
A measure of how far east or west a point on the Earth's surface is from the Prime Meridian (which passes through Greenwich, England). It is measured in degrees and ranges from -180° to +180°.
Latitude
A measure of how far north or south a point on the Earth's surface is from the equator. It is measured in degrees and ranges from -90° (South Pole) to +90° (North Pole).
Shapefile
A nontopological format for storing a homogeneous collection of points, lines, or polygons and associated attribute information. It can only store points or lines or polygons.
Spatial Data
A representation of the world using spatially referenced points, lines, and polygons. The vertices that form the shapes are X, Y coordinate pairs.
Cartography
A subdiscipline in information science that combines art and science to visually communicate spatial data through maps.
Inset Map
A supplementary map in a map layout. An example from cartography: a map layout of Rexburg has one supplementary map that shows Rexburg's location in Idaho and another supplementary map that zooms in on the BYUI ropes course to show greater detail.
GIS (Geographic Information System)
A system that captures, stores, analyzes, and displays geographic or spatial data. It allows users to understand and visualize patterns, relationships, and trends in data that are tied to specific geographic locations.
Attribute Table
A table that contains information about geographic features in a shapefile or feature class. The table contains records (rows) and fields (columns). For example, for a point feature class of cities, each record is a different city (for example, Rexburg, Idaho Falls, Salt Lake) and each field might be a different demographic (for example, population, average income, children under age 5, and so on).
Feature Class
A topological format for storing, in a geodatabase, a homogeneous collection of points, lines, or polygons and associated attribute information. For example, a polygon feature class for storing voting precinct information.
Nominal Data Level of Measurement
A type of qualitative data that consists of names or descriptions. No order or ranking is implied. An example from GIS is a feature class with an attribute for airport names. This data type is sometimes used to label features in a map.
Ordinal Data Level of Measurement
A type of qualitative data that is ordered on a hierarchical scale, such as highest to lowest, smallest to largest, and first to last. An example from GIS is an airport feature class with the attribute of size (from local to international). Symbology can be used to reflect the ranking.
Interval or Ratio Data Level of Measurement
A type of quantitative data that consists of numbers that imply a measurement or count. The numbers typically can be used in a calculation. Their data type is long, short, decimal, or float. It is never text. An example from GIS is an airport feature class attribute for the average length of the runways.
Database Key
A value in one table that matches a value in another table and allows the two tables to connect. As an example, your I-Number is a unique attribute identifier that connects you to many different tables such as student major and year in school.
Dissolve
A vector data management tool that aggregates features in one feature class based on a specified attribute. It simplifies the data.
Union
A vector geoprocessing tool that combines two polygon feature classes into a new feature class. All features and their attributes will be written to the output feature class. Use with caution.
Intersect (as a geoprocessing tool)
A vector geoprocessing tool that creates a new feature class from the overlap between two feature classes. The attribute table includes attributes from both input features. Input features can be points, lines, or polygons.
Text data type
Alphanumeric symbols that may or may not form coherent words. It is used to record addresses, descriptions, or notes, and numbers that represent codes. Examples: 'Snake River,' 'H135,' and '2760.'
Proximity Analysis
An analysis that determines the proximity or distance between features in a GIS dataset. It is used to assess spatial relationships, identify nearest neighbors, and analyze spatial patterns.
Map Legend
An area set aside on a map that shows the meaning of the symbols colors and styles used to represent geographic data on the map.
Spatial Join
Attaches attributes from one feature to another based on the spatial relationship. An example from GIS would be to attach to railroad lines in Europe with the names of the countries they cross.
Quantitative data
Attributes that can be counted, measured, and represented by a number that has mathematical value. As an example in GIS, a feature class of rivers might have the attribute 'river length.'
Merge
Combines multiple feature classes into a single, new output feature class. If you don't want to create a new feature class, use the 'append' tool. The feature classes should have the same geometry and theme. For example, combine a city point feature class to another city point feature class.
Spatial Data
Data that is associated with specific geographic locations or positions on the Earth's surface. It includes information about the shape, size, location, and attributes of geographic features.
Short Integer, Long Integer, Float, Double, Text
Different data types used to represent numerical values or text in a GIS.
Data Levels of Measurement (i.e., Ordinal, Nominal, Interval, Ratio)
Different ways of categorizing data based on the level of measurement and the properties of the data.
Choropleth Map
Displays rate and ratio data as polygons shaded with colors that depict changes in values. Typically, the colors are the same hue that darkens with changes in values. An example is literacy rate data for the world's countries shaded with colors from pale green (high rates) to dark green (low rates).
Standard Deviation
Divides data into classes based on the standard deviation from the mean. This method is sensitive to outliers.
Equal Interval Classification Method
Divides the number of records in a feature layer into groups such that the attribute values are divided into equal size ranges.
Overlay Geoprocessing
Geoprocessing that answers the basic GIS question "What's on top of (or within) what?" For example, which land parcels are within the 100-year floodplain. Intersect and union are common geoprocessing tools used in this type of analysis.
Proximity Geoprocessing
Geoprocessing that answers the basic GIS question "what's near what?" For example, which wells are near a hazardous waste site. Buffer is a common geoprocessing tool used in this type of analysis.
Quantile Classification Method
Grouping or categorizing objects using specific criteria. As an example in GIS, using map symbology to group population density of world countries into 5 categories. Divides the number of records in a feature layer into groups such that each grouping (also called a class) has approximately the same number of records.
Value
How light or dark a color is with no change in hue. An example from cartography: variations in lightness and darkness of the color blue might be used to depict water depth.
Boolean statement
Includes a conditional operator, and, or, not and returns a true or false. As an example, at BYUI the statement 'students under age 20 and Female' will return fewer values than 'students under age 20 or Female.'
Discrete Features
Individual, distinct geographic elements that can be represented as points, lines, or polygons. For example, a city or a building.
Attributes
Information about a geographic feature. For example, information about airports might be the elevation or the type (regional or international).
Attribute Data
Information about the characteristics or attributes of geographic features. It is typically stored in tables and linked to spatial data through a unique identifier.
Long Integer
Larger positive and negative integers that lie between -2,147,483,648 to 2,147,483,647. For example, -45,000 and 670,328.
Vector Data Model
Objects with known or definable boundaries. It is easy to define where the object begins and ends. Examples include buildings, roads, land parcels, and rivers.
Z-values
Often indicates elevation. It also can represent the value such as temperature, pollutant concentration, or slope especially when working with continuous surfaces.
Double data type
One of the data types used to represent fractional numbers with decimal places. Use this if there are between seven and 15 digits in the number. For example, 12.34567 and 0.1234567. If there are more than 15 digits, the computer rounds to 15 and uses a notation E+n where n represents the placement of the decimal point.
Float data type
One of the data types used to represent fractional numbers with decimal places. Use this if there are six or fewer digits in the number. For example, 12.3456 and 0.12345 are acceptable.
Lines
One-dimensional objects created by connecting multiple x,y points. Examples are rivers, trails, and roads. They have location and length.
Scale Bar
Provides a visual indication of distance and feature size on a map. It is typically divided into parts and is labeled with its ground length, for example, 5 miles.
interquartile range
Q3-Q1
Classification Methods
Quantile, Equal Interval, Natural Breaks (Jenks), Standard Deviation, Geoprocessing
Varience
S^2 = (Sum(x-x`)^2)/n
Attribute Query ('select by attribute')
Selects a subset of map data by attribute values. The process in ArcGIS is called 'select by attribute,' and it operates on one layer or table. For example, select for a roads feature calls all highways with more than four lanes. This operation does not create a new feature class.
Spatial Query ('select by location')
Selects a subset of map features found in one feature layer by its relationship to features in another layer. The process in ArcGIS is called 'select by location.' This process does not create a new feature class. For example, select a subset of buildings within a distance of a park.
Intersect (as a spatial query)
Selects a subset of map features that cross or are found within another map layer. For example, given a highway feature class and a Native American lands feature class, this process could select the subset of highways that cross Native American lands.
Short Integer data type
Smaller positive and negative integers that lie between -32,768 and 32,767. For example, -10,238 and 235.
Standart Deviation
Sqrt(Varience)
Pictorial Symbols
Symbols that use pictures to aid interpretation. An example from cartography: use an airplane to depict an airport.
Proportional Symbols
Symbols that use size to differentiate their value. An example from cartography: different sizes of airplane symbols indicate whether an airport is regional, national, or international.
Attribute Join
The GIS process that is used to attach a non-spatial data table to the attribute table of a feature class or shapefile. Both tables must have a common attribute key. An example is attaching a cost-of-living table to a polygon feature class of cities.
Mean
The average of a set of numbers
Points, Lines, Polygons
The basic geometric shapes used in a vector data model to represent geographic features. Points are used for single locations, lines for linear features, and polygons for areas or regions.
Hue
The dominant wavelength of color depicted by the percent of red, blue, or green. An example from cartography: blue might be used to depict water.
Annotation Feature Class
The geodatabase name for map text. Includes the text string, and other properties such as the shape points for placing the text, its font type, color and size.
Classification
The process of categorizing data into groups or classes based on similar characteristics or values.
Data Generalization
The process of reducing detail while preserving important characteristics when moving from large scale maps with more detail to small scale maps with less detail.
Map Scale
The ratio between distance on a map and a corresponding distance on the ground. For example, on a 1:10,000 map, 1 cm on the map equals 10,000 cm (100 m) on the ground.
Geoprocessing
The set of operations and tools used in GIS to manipulate and analyze geographic information. It includes operations like overlay, buffer, and spatial analysis.
Polygons
Two-dimensional objects composed of lines that "close." The starting and ending vertices share the same location. Examples are political boundaries, lakes, and parks. They have location, length (perimeter), and area.
Natural Breaks (Jenks)
Uses an algorithm to find natural groupings in the data. It minimizes the variance within groups and maximizes the variance between groups. Groups the records in a feature layer into classes based on relatively large jumps between attribute data values. This is not useful for comparing multiple maps built from different underlying information.
Continuous Surfaces
Values that vary smoothly across an area without abrupt or well-defined breaks. Examples include representation of a) a measured concentration level such as rainfall or temperature; b) values measured from a fixed point such as elevation above sea level; and c) a measured concentration emitting from a fixed point in space such as oil spreading from a leaking pipe.
Qualitative
qualitative data is categorical and non-numeric (e.g., colors)
Range
the difference between the highest and lowest scores in a distribution
Median
the middle score in a distribution; half the scores are above it and half are below it
Mode
the most frequently occurring score(s) in a distribution
