Unit 3 – geographic information system (gis)
1. GIS “Geographic Information System”. A GIS is an information system which handles geographic information. GIS is more than just a special kind of information system. It is a technology. A technology is “the whole body of1 methods and materials (документация, средства) used to achieve the stated objectives”. GIS technology is often confused with other sciences and technologies that deal with spatial data handling. These include: remote sensing, cartography surveying, geodesy, photogrammetry, and of course, the “father” science to GIS, geography.
2. A GIS is an organized collection of2 computer hardware, software, geographic data, and personnel designed to efficiently capture, store, update, manipulate, analyse, and display all forms of geographically referenced information3. It (GIS) is a computer system manipulating geographic data. Geographical data describes objects from the real world in terms of:
the object’s position with respect to a known coordinate system;
the object’s physical attributes associated with the geographical position;
the spatial relationship of the object with surrounding geographical features4 (topology).
3. Spatial Information Theory. Spatial information is always related to geographic space, i.e., large-scale space5. This is the space beyond the human body, space represents the surrounding geographic world (географ. пространство). Within such space, we constantly move around, we navigate in it, we conceptualise it in different ways. Geographic space is also the space of topographic and cadastral features (зд. характеристик объектов). Geographic space is distinct from small-scale space, or “table-top” space6. Geographic information technology is used to manipulate (выбор и анализ) objects in geographic space and to acquire knowledge from spatial facts (данные).
4. Geographical information is a unity of spatial and attribute (non-spatial) information describing an entity, e.g., the coordinates of the centre of the gravity, the identifier (ID), the address and the building year of a house. Spatial information contain coordinates, coordinate system, spatial accuracy, and geometric and topological information of an entity. Attribute information contain identifying, linking, timing and describing information of an entity, e.g. the ID, the address, the building year and colour of a building. An entity is a thing in the real world with an independent existence. The distinction between spatial and attribute information is largely arbitrary; both spatial and attribute information describe dimensions of an entity7.
5. So, just what is a GIS? GIS is a powerful set of tools8 for collecting, storing, retrieving at will, transforming, and displaying spatial data from the real world. Spatial data are data which represent objects that have physical dimensions – they take up space. Geographic spatial data occur on, in, or above the planet Earth. In the context of GIS technology, spatial data are landscape features which can be represented on a map. Spatial data occur in three forms: points, lines, and polygons or areas. In two-dimensional space, there exist no other alternatives. A soil type or forest stand appears on the land as a polygon. Rivers and roads are lines (or very narrow polygons), and wells, stream intersections, or eagle nests are points. All features of the landscape can be reduced to9 one of these three spatial data categories. This is an important concept because GIS technology is a computer technology. To use computers for handling spatial data, we must reduce our data to the computer’s level of comprehension10. We must specify three things for the computer. (1) Where each feature is in geographic space, (2) What each feature is, and (3) What is each feature’s spatial relationship to other features on the map.
6.The history of GISs started from “computer-mapping” programs in the early 1960s. The Harvard Graphic Laboratory was one of the most effective research groups developing computer-based map analysis programs. The fundamental components of a GIS and its environment (GIS-environment) are:
Input (a data input subsystem which collects and/or processes spatial data derived from existing maps, remote sensors, etc.).
Data storage and retrieval (a data storage and retrieval subsystem which organizes the spatial data in a form which permits it to be quickly retrieved, as well as permitting rapid and accurate updates and corrections11).
Manipulation (a data manipulation and analysis subsystem which performs a variety of tasks).
Output (an output which is capable of displaying all or part of the original database).
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GIS facilities |
7. One more important thing we must tell the computer is what various spatial features are. The labels we attach are called attributes, and landscape features can have an unlimited variety. For example, a lake may be described by its name, depth, water quality, fish populations, chemical composition, color, bottom contour, algal levels, salinity, taste, biological productivity, ownership, etc. As new information is required, it must be added to the GIS database. Furthermore, as we use the GIS we may transform data already in the database to produce new information internally12. For example, fish population sizes, productivity levels, access, and other factors might be combined to set catch limits of fish species, which in turn become new attributes describing the lake.
8. The power of GIS is most apparent when the quantity of data involved is too large to be handled manually. The ability to perform complex spatial analysis rapidly provides a quantitative as well as qualitative advantage. The GIS offers a practical means to manage large and diverse spatial data base and provides effective tools to understand the relationships among diverse phenomena. The GIS has not only made the production and analysis of geographic information more efficient it is changing the way geographic information is perceived and used13. It is a technology that makes geographic data more malleable.
9. Despite the analytical power of this technology, a GIS, like any other system, does not and cannot exist on its own14. To be successful it must exist within a suitable organizational framework15. There must be an organization of people, facilities and equipment responsible for implementing and maintaining the GIS. Ultimately, a GIS is used to produce information that is needed by a user. The client may be a person or a group of people. To be useful to the client, information must be of the right kind and quality, presented in an appropriate format to the client to use and to be available at the right time. The GIS is operated by staff who report to a management16. That management is given the mandate to operate the GIS facilities17 in such a manner as to serve some user community within an industry, business, or government organization.
10. The data used in a GIS represent something about the real world at some point in time18. The most important aspects of data quality are: accuracy, precision, time, currency and completeness. The information in a GIS is represented in two basic forms: as maps and as tables. What distinguishes a GIS from other systems is the ability to integrate georeferenced data19. GISs are a powerful resource that provide flexible methods for exploring relationships among geographic data and assisting experts from diverse fields in pooling knowledge to solve complex problems, and to assist the users in accomplishing the goals of their respective organizations.
Notes:
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1. …the whole body of… |
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2. …an organized collection of… |
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3. …geographically referenced information |
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4. …surrounding geographical features |
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5. …large-scale space |
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6. …small-scale space, or “table-top” space |
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7. …dimensions of an entity |
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8. …a powerful set of tools… |
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9. …can be reduced to… |
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10. …we must reduce our data to the computer’s level of comprehension |
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11. …accurate updates and corrections |
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12. …internally |
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13. …geographic information is perceived and used |
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14. …cannot exist on its own |
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15. …within a suitable organizational framework |
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16. …staff who report to a management |
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17. …to operate the GIS facilities… |
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18. …something about the real world at some point in time |
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19. …the ability to integrate georeferenced data |
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