Maps and Attributes
Maps have always been powerful medium of representing information. A GIS is the ultimate system that uses maps to make decisions and provides valuable insight. Suppose you are given the task of determining where, in a particular region, a new town should be developed from scratch in the wilderness (but not too far from civilization) that will be used to house people with various connections to opening a major new mine extracting uranium ore. After pondering the problem, you conclude that the best way to start would be to acquire some maps that include the areas near the eventual mine. These maps could include the following thematic types:
Hazardous waste sites
Hydrology and floodplains
Not only would maps of these features be required, but additional information in the form of more details about these would be essential. When all this is collected, what do you do? You lay out the maps, become familiar with their contents, and start looking for potential sites proximate to the future mine. You shift back and forth from map to map trying to find appropriate clues as to where the best site(s) would be. This requires a sort of mental overlay process, which is difficult. After narrowing possibilities, you then feed in pertinent ancillary information. Finally, you arrive at a decision, but this is still subjective and based largely on a qualitative assessment. The whole process is cumbersome, tedious, and generally inefficient.
But what if there is some kind of "automated decision making" that allows you to systematically combine the information in individual maps into an interrelated composite that handles diverse data, embellishes that with relevant ancillary data, and then uses a logical program that quantifies the process of final choice as to the most optimal location. That is precisely what GIS is all about. GIS is the outgrowth of the computer age, and the ease with which data can be manipulated by scanning and other input methodology. GIS centers on maps and other kinds of spatial displays - the starting point in our discussion of this new technology.
Maps share a common characteristic: they are visual, miniaturized representatives, or surrogates, of places and classes of features located geospatially on or above the surface, be it land or water. They thus depict aspects of the local, regional, or global geography, which we can locate geometrically in an x, y (horizontal), and z (vertical) plot. We can then reference the plot to some form of coordinate and projection system. A map projection is a specific way of transferring points or locations from a spherical globe onto a scaled-down flat surface (the map) according to a systematic, orderly realignment, using a latitude/longitude grid network.
Photos (images) and maps are inherently two-dimensional or planimetric, although we can use techniques, such as contours or shading, to present a quasi-three-dimensional appearance or to extract information about relative elevations above generalized datum planes. The most common type of three-dimensional map is the topographic map. Maps in general nearly always have the following, essential information:
Graphic distance measures
Orientation and direction
Projection type, and
A geographic coordinate system
along with other descriptors and symbols in an accompanying legend. Topographic maps also have contour intervals.
Maps represent features of the ground in their correct spatial positions. Further information about these features can be presented in the form of themes. We also refer to these themes as attributes, which are general descriptors that are inherently non-spatial (they depend on characteristics rather than the location). A parcel of land, regardless of size, likely contains a diverse mix of features or characteristics that we can assign to different categories; in other words, it has many attributes. We may need a wide variety of thematic maps and associated attributes to fully describe the contents of a surface. Thus, given an area of, say, one square kilometer, one map may display road networks, another vegetation cover, a third dwellings or functional buildings, a fourth engineering properties suited for excavation, and so forth. We may combine several themes on a multipurpose map, such as show together roads, buildings, recreational areas, etc. One common type of map shows land cover, which identifies all appropriate classes or categories that we wish to display within the map scale limits at selected points or locations. A variant of this map is the land use map that differs by detailing aspects of the cover involved in, or of interest to, human activities.
A GIS combines the power of maps, satellite images, and aerial photographs with databases that store information behind the maps and images. One way to think about GIS is to break it up into its three initials. The “G” part of GIS could be a map or an image. The “I” part of GIS is the Information, or the database, containing attributes behind each map feature. This could be the magnitude of an earthquake, for example, or the population of a country. The “S” part of GIS is invisible to the user, but this Systems part makes it possible to analyze the maps and attributes together.
Map features and their attributes may be subjected to many different operations like querying, sorting, changing legends, creating buffers, and others. GIS requires certain kinds of spatial and attribute data. These are produced by national governmental organizations such as the Survey of India, the Geological Survey of India, the Central Groundwater Board, the Census of India, the Ministry of Agriculture, and others, as well as tribal, state, and local government, nonprofit organizations, and private industry. However, the most important component of a GIS is the user. It is the person that must make sense of what the GIS tools and methods are saying, and it is the person who must decide what action to take.
This website is hosted by
Department of Geology
Aligarh Muslim University, Aligarh - 202 002 (India)