Mini-Glossary of Geospatial Terms

  • Pixel – is the smallest unit of a digital image or graphic that can be displayed and represented on a digital display device. A pixel is the basic logical unit in digital graphics. Pixels are combined to form a complete image, video, text or any visible thing on a computer display.
     

  • Cluster Analysis – a statistical technique that allows users to identify areas that are similar in some sense
     

  • Geographically Weighted Regression – a statistical technique that allows users to identify trends in observations and processes that may be spatial in nature
     

  • Hyperspectral Datasets – imagery with multiple bands of spectral data covering narrow frequencies; a traditional multispectral dataset has 4 spectral bands each covering a frequency range of a hundred to several hundred nanometers, versus hyperspectral data which can have 256 spectral bands each covering only a single nanometer of the spectrum
     

  • NVDI – a simple analytic technique to assess the health of vegetation, it is calculated as:  (Near Infrared – Red) / (Near Infrared + Red)
     

  • Object-oriented Classification – an advanced remote sensing technique that identifies clusters of similar pixels based on spectral and spatial characteristics as opposed to traditional unsupervised classifications which identify similar pixels based only on their individual spectral characteristics
     

  • Spatial Overlay – a mathematical technique for spatial analysis whereby users assign weighting values to a set of spatial layers and then sum these values for a comprehensive ranking system
     

  • Orthorectification – is the process of removing the effects of image perspective (tilt) and relief (terrain) effects for the purpose of creating a planimetrically correct image. The resultant orthorectified image has a constant scale wherein features are represented in their 'true' positions.
     

  • Mosaicing – is blending together of several arbitrarily shaped images to form one large radiometrically balanced image so that the boundaries between the original images are not seen.
     

  • Digital Elevation Model (DEM) – is a representation of a terrain's surface created from a terrain's elevation data.
     

  • Radiometric Resolution – refers to how much information is in a pixel and is expressed in units of bits. A single bit of information represents a binary decision of yes or no, with a mathematical value of 1 or 0.
     

  • Spatial Resolution – is a term that refers to the number of pixels utilized in construction of a digital image. Images having higher spatial resolution are composed with a greater number of pixels than those of lower spatial resolution.
     

  • Map scale – refers to the relationship (or ratio) between distance on a map and the corresponding distance on the ground. For example, on a 1:100000 scale map, 1cm on the map equals 1km on the ground.
     

  • Map Projection – is a way to flatten a globe's surface into a plane in order to make a map. This requires a systematic transformation of the latitudes and longitudes of locations from the surface of the globe into locations on a plane.
     

  • Datum – is a model of the earth that is used in mapping. The datum consists of a series of numbers that define the shape and size of the ellipsoid and it's orientation in space. A datum is chosen to give the best possible fit to the true shape of the Earth.
     

  • Universal Transverse Mercator (UTM) – is a system for assigning coordinates to locations on the surface of the Earth. Like the traditional method of latitude and longitude, it is a horizontal position representation, which means it ignores altitude and treats the earth as a perfect ellipsoid.

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