Geographic Information Systems (GIS) Vocab

The vocab from my GIS class

Geographic information systems (GIS)

Computerized systems used for storing, retrieving, manipulating, analyzing, and displaying geospatial data

Geospatial technology

Various high-tech systems that process location-based data

Remote sensing

Measuring an object’s characteristics from a distance using reflected or emitted electromagnetic energy, includes satellite images and aerial photography

Global positioning system (GPS)

Uses signals from satellites in Earth’s orbit to acquire real-time location information

Geography

The study of spatial variation (how and why things differ from place to place on the surface of the Earth)

Cartography

The science and art of making maps

Datum

A reference surface of the Earth from which a coordinate system can be calculated

Geographic coordinate system

Models the Earth as a 3D object and uses latitude and longitude, measured in degrees, as its unit of measurement

Planar coordinate system

Models the Earth as a 2D surface, like a map; the units of measurement vary, but often are in meters or feet

Lines of latitude (parallels)

Run east-west and give the location of points north or south of the Equator (which is 0 degrees N/S)

Lines of longitude (meridians)

Run north-south and give the location of points east or west of the Prime Meridian (which is 0 degrees E/W)

Graticule

The latitude/longitude grid

Conformal

A projection type that preserves shapes and angles

Equivalent/equal area

A projection type that preserves area (size of objects)

Equidistant

A projection type that preserves relative distances between points on the Earth’s surface

Azimuthal (“true direction”)

A projection type that preserves direction from a central point

Compromise

A projection type that attempts to optimize Earth’s features by limiting major distortion, but by doing so, does not preserve any specific features

Developable surface

Geometric shapes which Earth’s shape is projected onto; can be conic (a cone), cylindrical, or planar (azimuthal)

Aspect

The relationship between the axis of the Earth and axis of the projection; can be equatorial (“normal”, oriented N-S), transverse (oriented E-W), oblique (neither N-S or E-W); and polar (centered on a pole)

Contact

How the surface “touches” the reference globe; determines the point of least distortion

Tangent contact

Developable surface touches the Earth along a single line or point

Secant contact

Developable surface touches the Earth at 2 lines or points

Geographic scale

The real-world size or extent of an area

Map scale

The relationship between measurements made on a map and their real-world equivalents

The main components of GIS

Hardware, software, data, network, procedures, and people

Vector data

Consists of points (coordinates), lines (a series of coordinates), and polygons (space contained within a set of lines)

Raster (cell-based) data

Uses a grid where each cell on the grid is a pixel on the computer display; each cell is associated with a number, which determines how it will be displayed on a screen

Passive remote sensing

Refers to when a sensor does not emit any energy towards an object; it simply measures and records reflected and emitted reflected imagery (ie aerial photography)

Active remote sensing

Consists of directing energy towards a target and recording the energy, which is reflected back towards the sensor (e.g. radar, LiDAR)

Electromagnetic energy (light) 

Consists of both waves and particles 

The four components of remote sensing

Target (the object reflecting the energy), energy source (e.g. the sun, radar), transmission path (what does the energy source travel through?), and sensor (the tool that collects and records the energy emitted by the target, such as on a satellite

Incident radiation

Refers to the total amount of energy that strikes an object

Spectral signature

The ratio of reflected energy to incident radiation on an object; this can help us identify objects on maps

Color composite 

An image formed by placing a band of imagery into color guns associated with each of the three primary colors (RGB) to view an image in color rather than grayscale 

Standard false color composite

Near-infrared is in the red color gun, red is in the green color gun, and green is in the blue color gun

Spatial resolution

Refers to the area of Earth represented by each pixel

Spectral resolution

The number of bands measured by sensors; finer resolution refers to more band discernment/able to identify more details in wavelength

Tone

The grayscale levels (from black to white) or range of intensity of a particular color

Shape

The distinctive form of an object

Size

The physical dimensions (length, width, and area from the ground) of objects

Pattern 

The arrangement of objects in an image 

Texture

Repeated shadings or colors in an image

Association

Information referring to the location of objects and their related attributes in an image

Relief displacement

The phenomenon when tall images appear to lean outward from the center of a photo towards the edge

Orthorectification 

A process which georeferences the image (if needed) and removes distortion to give the image “uniform scale”, used to get rid of relief displacement 

Digital orthophoto quadrangles (DOQs)

Computer-adjusted images of aerial photos in which the distortion caused by topography and camera tilts has been removed; it combines the image characteristics of a photo with the geometric qualities of a map (as in, it is georeferenced)

Temporal resolution

The length of time it takes a sensor to take an image and then return to that same location to take another image 

Radiometric resolution

The degree of a sensor’s ability to determine differences and fluctuations within a band of light (as opposed to referring to how many bands can be discerned, which would be spectral resolution)

Geostationary orbit

Orbit precisely follows the direction and speed of Earth’s rotation so that it is always above the same point on the ground (sometimes called “geosynchronous orbit”)

Near-polar orbit 

Orbit passes near North and South poles while the Earth rotates; allows for near-global coverage 

Sun-synchronous orbit

A type of polar orbit set up so that the satellite always crosses the same areas at the same local time

Swath width

The width of the ground area a satellite is imaging as it passes over Earth’s surface

Along-track scanning (“pushbroom”)

Uses a linear scanner array to collect data

Across-track scanning (“whiskbroom”) 

Uses a rotating sensor that collects data by moving the sensor back and forth across the swath

Landsat Program

Began in 1972 by NASA and USGS, currently consists of 9 satellites

MODIS Program

Refers to an instrument attached to two NASA satellites, Aqua and Terra; takes low spatial imagery but has a very wide swath width

SPOT (Systeme Pour l’Observation de la Terre) 

A series of satellites developed by the French government starting in 1986, since taken over by Airbus 

Vantor

Formally known as Maxar, which purchased the companies DigitalEye and Geoeye; offers very high-resolution (sub-meter) commercial satellite data, but it is not freely available