Review of geospatial technologies

Geospatial technologies including GIS, RS, and GPS are increasingly used in a variety of fields where data gathering for and information about places, objects, and processes are displayed and analyzed. Each of these technologies comprises vast fields of study and research, but the integration of these technologies provides considerable descriptive, predictive, and analytical power.

GIS can be described as a system comprised of software, hardware, and georeferenced geographic data used to describe, and/or analyze patterns and processes that occur at a variety of scales. GIS provides advanced spatial analyses targeting location, attributes, and relationships of geographic features that exhibit spatial relations including proximity, direction, and topology (Theobald, 2001). Proximity may be understood in terms of relative and absolute distances of features from each other. Directional information is associated with relative and absolute directions from one feature to another. Topology describes numerical relationships between geographic features as encoded by adjacency, linkage, inclusion, or proximity (Clarke, 2003).

Remote Sensing has been defined as "the science and art of obtaining information about an object, area, or phenomenon through the analysis of data acquired by a device that is not in contact with the object, area, or phenomenon under investigation" (Lillesand et al., 2008). Sophisticated passive recording devices flown aboard aircraft and satellite platforms obtain information about feature reflection, transmissivity, and absorption of energy from electromagnetic spectra. Other active devices like radar transmit microwave energy from an antenna then record information about the intensity of the radiation 'backskattered' by the surface (Lillesand et al., 2008).

GIS and RS spatial data structures can be categorized into vector and raster data types. Vector data are comprised of points, lines, and polygons while raster data is comprised of grid cells. In general, vector data are the data of choice for accurate mapping purposes and raster data are the data of choice for mathematical and probabilistic analyses. Integration of GIS and RS can occur on a variety of levels, but an obvious unifying characteristic of both disciplines is raster spatial data. Raster GIS data is generally created by the tessellation of geographic space via interpolation of points to a statistical grid surface or by simply subdividing geographic space into a regular grid. Figure 1 illustrates a polygon that has been tessellated into a square grid to create a raster data type. Remotely sensed data is often the product of information about reflected portions of the electromagnetic spectrum captured on a charge coupled device. The size of pixels generated via a digital to analog conversion process is predicated on several factors including the amount of land area covered by the Instantaneous Field of View and the height of the remote sensing platform above the earth. Both vector and raster data can be displayed, integrated, and analyzed using software-hardware platforms that can accommodate a wide variety of proprietary and open source data formats. The U.S. Global Positioning System includes a group of at least 24 satellites rotating the earth used to determine ground positions via 'satellite ranging'. Originally developed for defense purposes, locations of features or field observations can be determined very accurately using GPS methods. GPS has resulted in dramatic improvements in the ability to accurately locate features on earth and more effectively orient response and recovery personnel to specific sites, or accurately designate hazardous areas to be avoided.

Fig. 1. Tessalation of a polygon to create a raster data type

Polygon x Column

Fig. 1. Tessalation of a polygon to create a raster data type

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