Glossary
Name  

aspect  The direction the developable surface faces in relation to the geographic coordinate system. Normal; transverse, oblique 
altitude  the height of an independent object, such as an aircraft, above ground level (AGL) 
angular unit of measure  the selected units for measuring angles. Choices include degree and radians. 
Name  

benchmarks  Benchmarks are realworld locations which have been carefully surveyed with locations to match a specific geoid. 
Name  

Cartesian coordinate system  An equally spaced grid that exists in a single geometric plane where intersections of perpendicular lines are labeled with the count of units from a specified origin (0,0) point 
compromise  projections attempt to balance all of the distortions in one map. This means that none of the six are "perfect", but each one is is balance with the others, the idea being that no one place is grossly distorted in comparison to any other place on the map 
conformal  serve the purpose of preserving shape, distance, and bearing, at the expense of area and scale 
control point  aka: tie point mathematically derived points that connect a two spatial objects together, such as a geoid and a reference ellipsoid 
Name  

datum shift  when control points are adjusted via better mathematical calculations or realworld surveying. Benchmarks cannot move, but control points can change via datum shifts. ''Major'' Large effort; many points change; expensive and timeconsuming. Noted with a twodigit year (ie NAD83) ''Minor'' Just a few points change. Less expensive; less involved. Noted with a fourdigit year (ie. NAD83(1985)) 
degrees  measurement of plane angle, representing 1⁄360 of a full rotation (circle). In full, a degree of arc or arc degree. Usually denoted by ° 
developable surface  a geometric shape which will not be distorted when flattened. Used as the base shape to transfer features during projections. Most often a cone, cylinder, or plane (azimuthal) 
distortion ellipses  start as circles placed on the globe. As the projection is created, the distortion ellipses distort in a manner equal to the map's distortion at the place upon which they are centered. This method allows for a user to visualize the map's distortion without any measuring equipment. 
database  electronic storage container with a topdown structure in which the items contained are related to each other and that relationship allows for the data to be quickly and efficiently queried and retrieved for use. 
Distance Decay  A concept where the intensity of an effect (e.g., a crime's severity) decreases as the distance from the origin increases. 
Name  

Earthcentered, Earthfixed System  Earthcentered, Earthfixed systems use the center of the Earth as a start point for measurements, while localnorth systems use a smaller area affixed to the Earth's surface as the start point 
elevation  the vertical distance between local mean sea level and a single point on the Earth's surface 
Name  

geodesy  the science of measuring and monitoring the size and shape of the Earth and the location of points on its surface 
geodetic  an action relating to geodesy 
geodesist  a scientist who studies the size, shape, and changing surface of the Earth 
Geographic Information Systems  the software used to create, store, and manage spatial data, analyze spatial problems, and display the data in cartographic layouts 
geoid  a model of the variation between global mean (average) sea level and local mean sea level, which is used to measure precise elevations on the topographic surface 
geoid separation  
Geographic Information Sciences (GIScience)  the branch of geospatial sciences concerned with the underlying structure of how to collect and analyze data 
global mean sea level  the average of the sea level as affected by the pull of gravity when there is a finite amount of water upon a model of the Earth. 
Global Navigation Satellite System  a general term for the technology of using satellites and a signal receiver to pinpoint a location anywhere on the surface of the Earth 
geodetic datum  the result of attaching a "freefloating" reference ellipsoid to a specifically measured geoid via control points and benchmarks. 
geographic grid  the result of using an established angular unit of measure to label the intersections of northsouth and eastwest lines on the surface of the Earth starting the labels at a principal meridian 
Geographic Profiling  A process that uses the locations of a connected series of crimes to determine the most likely area of offender residence. 
Name  

horizontal datums  used to reference location on the Earth's surface, regardless of elevation 
Hot Spot Analysis  Identification of areas with a high concentration of features. 
Name  

spatial resolution  the realworld measurement of one side of one pixel in a raster, ie. 30 meters. High spatial resolution would equate to small pixels while low spatial resolution would equate to large pixels 
seconds  arc minute. 1/60th of an arc minute; 1/3600 of a degree. Usually denoted by ' 
small scale map  a map where the representative fraction is far from one and the objects in the map are relatively small (zoomed out) 
spheroid  a spherelike 3D object where the radius in one direction is longer than the radius in a direction at a right angle to the first 
State Plane Coordinate System (SPCS)  a planar coordinate system for the United States which breaks states into zones and uses either a Lambert Conformal Conic projection (eastwest trending states) or a Transverse Mercator projection (northsouth trending states) to create small pieces with little distortion. The zones are stitched together to create a US wide map. 
statement of equivalency  (also known as ''verbal scale''): the relative scale is expressly defined on a map: 1 cm = 1 kilometer; 1 inch = 10 miles 
Seven Part Model of GIS 

Spatial Data  Data that deals with location, such as lists of addresses, the footprint of a building, the boundaries of cities and counties, etc. 
Spatial Thinking  The ability to draw upon past experiences and apply them to a new problem utilizing space, the distribution of objects in the real world, and a means of representing those objects. 
Spatial Statistics  Probability and distribution of spatial data to determine patterns. 
Name  

Lambert Conformal Conic Projection  projection developed by Johann Heinrich Lambert in 1772 utilizing a conic developable surface designed to preserve shape and size (to conform) of land masses. 
large scale map  a map where the representative fraction is close to one and the objects in the map are relatively large (zoomed in) 
latitude  also known as 'parallels' the eastwest portion of a geographic grid measured with angles between 0 and 90° 
local mean sea level  the measurement above or below the global average at a single point on the Earth's surface used for recording the elevation of topographic surface's relief 
landforms  the descriptive words for individual features on the topographic surface, such as "hills", "valley", and "ridgelines" 
Name  

map distortion  In GIS, the unavoidable inaccuracies which occur when transferring features from a geographic coordinate system to a developable surface. Comes in six flavors:

map scale  a mathematical representation expressing distance on a map vs distance on the ground 
minutes  "arc minute" 1/60th of a degree. Usually denoted by " 
modern geodesy  precise global and regional locations, both horizontal and vertical (along the Earth and above the Earth), mapping the land sea, and ice, and determining the variations in the Earth’s gravitational pull and how this effects measurements 
Mercator Projection  a projection developed by Gerardus Mercator in 1569 utilizing a cylindrical developable surface and a normal aspect tangent at the Equator and designed to produce a map with parallel lines of longitude and latitude. The main purpose of this projection is navigation in the midlatitudes for eastwest travel. 
Multiple Ring Buffers  A series of concentric rings used in spatial analysis to represent distances from a point. 
Name  

normal aspect  when a developable surface is tangent or secant with a line of latitude (parallel) Polar: when an azimuthal developable surface is tangent with either of the poles Equatorial: Specifically tangent with the Equator 
NonSpatial Data  Attributes related to a location but not describing its physical placement in space, such as information about a tree's age, type, and health. 
Name  

oblate spheroid  a spherelike object which is wider than it is tall 
oblique aspect  all other orientations after normal and transverse. Not tangent/secant with either a line of latitude or a line of longitude 
orthometric datums  shows the changes in the Earth's gravitational pull from 0  any height referenced to the Earth's gravity field can be called as "geopotential heights" 
orthometric height  the measured distance between the geoid and the topographic surface. 
Name  

planar coordinate system  the result of converting an angular unit of measure used to locate objects on a geographic coordinate system to a linear unit of measure via a Cartesian Coordinate System. Planar Coordinate Systems utilize linear units such as feet, meters, and international feet. 
Prime Meridian  the name of the principal meridian in the latitude/longitude system 
principal meridian  the northsouth line from which the labeling begins. Eastwest lines have a very obvious start point: the equator. Northsouth lines must start somewhere, so when it is established for a particular geographic grid, it can be considered the principal meridian. 
projection  technically: the result of using one of variety of methods to transfer the geographic locations of features from a geographic coordinate system to a developable surface everyday use: any coordinate system, geographic or projected 
prolate spheroid  a spherelike object which is taller than it is wide 
Predictive Analysis  A process of analyzing current and historical facts to make predictions about future or otherwise unknown events. 
Name  

reference ellipsoid  an ellipsoid that is drawn to bestfit an area. World reference ellipsoids are drawn to bestfit the entire geoid; local ellipsoids are best fit on one side to a single place of the geoid 
relief  the difference between the highest and lowest point within a particular area while landforms are the descriptive words for individual features 
representative fraction  expression of map scale in ratio form utilizing nonspecific linear unit, such as 1 map unit equals 250,000 real world units, or 1:250,000 
Name  

three dimensional datums  combine horizontal datums with ellipsoidal height 
tidal datums  show the changes in sea level due to tides and are based on local mean sea level 
tie points  see Control Points 
topographic surface  a detailed map of the surface features of land. It includes the mountains, hills, creeks, and other bumps and lumps on a particular hunk of earth. The word is a Greekrooted combo of topos meaning "place" and graphein "to write." 
transverse aspect  when a developable surface is tangent or secant with a meridian 
Transverse Mercator Projection  a variation of the Normal Mercator Projection where the tangential line is switched from a parallel to a meridian. Lines of longitude and latitude appear circular and the map is optimized for northsouth travel. 
trilateration  the process of determining absolute or relative locations of points by measurement of distances, using the geometry of circles, spheres or triangles. ... In contrast to triangulation, it does not involve the measurement of angles 
true direction maps  equidistant maps specifically for azimuthal projections 
Name  

Universal Transverse Mercator (UTM)  a Planar Coordinate System (via a projection) which divides the globe into 60 separate 6° wide zones, each one with the principle meridian 3° from either side and cut half at the Equator. Each strip, or zone, is then stitched together to create an entire Earth flat map. To prevent negative numbers, each zone is assigned a origin arbitrarily labeled 500,000 mE, 10,000,000 mN. Using a Cartesian Coordinate System, locations are measured in meters. Since both the north and the south half of each zone will contain the same coordinates, and there are 60 zones, all possible coordinate pairs will appear 120 times, forcing the need to use the zone number and designate North or South is needed. 
Name  

vertical datums 

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spatial aspect  Associating the idea or property of where with data to be analyzed. 
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geospatial sciences  A discipline that focuses on using information technology to understand people, places, and processes of the earth. Spatial analysis of human and physically variables is fundamental to the discipline. 