What is GIS?
Geographic Information System (GIS) is a comprehensive subject, combining geography and cartography, remote sensing and computer science. It has been widely used in different fields. It is a computer System used for inputting, storing, querying, analyzing and displaying Geographic data. With the development of GIS, GIS is also called “Geographic Information Science”, and in recent years, GIS is also called “Geographic Information Service”. GIS is a computer – based tool that can analyze and process spatial information. GIS technology integrates the unique visual effects and geographic analysis functions of maps with general database operations.
GIS component
GIS can be divided into the following five parts: Personnel, is the most important component of GIS. Developers must define the various tasks to be performed in GIS and develop handlers. Skilled operators can often overcome the shortcomings of GIS software, but the opposite is not true. The best software cannot compensate for the operator’s ignorance of GIS. Data, precise and available data can influence the results of queries and analyses. Hardware, hardware performance affects the software to the data processing speed, easy to use and possible output mode. Software, including not only GIS software, but also a variety of databases, mapping, statistics, image processing and other programs. Process, GIS requires well-defined, consistent methods to produce correct, verifiable results. GIS is a kind of information system, which is different in that it can operate and process geo-referenced data. Geographic reference data describes the location and attributes of spatial elements on the earth surface. There are two geographical data components in GIS: spatial data, which is related to the geometric characteristics of spatial elements; Attribute data provides information about spatial elements. Geographic information and geographic data are both related and different.
Geographic data and geographic information
Information, in the narrow sense of information theory, is defined as “the difference between two uncertainties”, that is, the difference of people’s understanding of things before and after obtaining information; The generalized information theory holds that information refers to a form of mutual connection between subject and external object, and is all useful information or knowledge between subject and object. We think that information is to provide people with knowledge about new facts in the real world through some media. It comes from data and does not change with the carrier. It has the characteristics of objectivity, practicability, transmission and sharing. Data, qualitative and quantitative description of a target of the original data, including text, numbers, symbols, language, images, images, etc., it has the characteristics of identification, storage, expansion, compressibility, transmissibility and conversion. Information and data are inseparable, information comes from data, data is the carrier of information. Data is the representation of objective objects, while information is the meaning contained in data, the content and interpretation of data. Data is processed in order to get the information contained in the data. Data contains raw facts. Information is the result of data processing, the processing of data into a meaningful and useful form. Geographical data is a symbolic representation of the relations between various geographical features and phenomena, and refers to the sum of numbers, words and images that represent the quantity, quality, distribution characteristics and rules of elements in the geographical environment. Geographic data mainly includes spatial location data, attribute characteristic data and time domain characteristic data. Spatial location data describes the location of geographical objects, which includes both the absolute location of geographical elements and the relative location relationship between geographical elements. Attribute data, sometimes called non-spatial data, is a qualitative or quantitative indicator describing the characteristics of specific geographical elements, such as the grade, width, starting point and end point of a highway. Time domain characteristic data is to record the time or period of geographic data collection or occurrence of geographical phenomena. Time domain characteristic data is very important for environmental simulation analysis and is being paid more and more attention in the field of geographic information system. Spatial location, attribute and temporal characteristics constitute three basic elements of geospatial analysis. Geographic information is the meaning contained in geographic data, the information about a specific location on the earth’s surface, the characterization and all useful knowledge about the nature, characteristics and movement of geographical entities. As a special kind of information, geographic information not only has the basic characteristics of general information, but also has regional, spatial and dynamic characteristics. GIS data represent real world objective objects in the form of digital data. Objective objects in the real world can be divided into two abstract concepts: discrete objects and continuous object fields. There are two main methods to store data in GIS system: raster (grid) and vector.
Grids and vectors
Raster data, consisting of rows and columns that hold a unique value store. It is similar to raster images in that, in addition to using appropriate colors, the values recorded by individual cells may also be a classification group, a continuous value, or a null value recorded when the data is not available. The resolution of the raster data set depends on the grid width of the ground unit. Usually a storage cell represents a square area of the ground, but it can also be used to represent other shapes. Raster data can be used to represent either an area or a physical object. Vector data uses geometric shapes such as points, lines, or surfaces to represent objects. Vectors can also be used to represent fields with continuous variability. Use contour lines and irregular triangular grids to represent altitude or other continuously varying values. The TIN record evaluates the points connected into an irregular grid of triangles. The surface of the triangle represents the topographic surface. Because digital data is collected and stored in different ways, the two data sources may not be fully compatible. So GIS must be able to transform geographic data from one structure to another.
System transformation
Map data in GIS must be able to be manipulated to align or coordinate with data obtained from other maps. Before digital data can be analyzed, they may undergo other processes that integrate them into GIS, such as projections and coordinate transformations. The Earth can be represented by many models, each of which may give a different set of coordinates (e.g. latitude, longitude, elevation) for any given point on the earth’s surface. The simplest model assumes that the earth is an ideal sphere. As more measurements of the Earth accumulate, models of the earth become more sophisticated and accurate. In fact, some models are applied to different regions of the earth to provide greater accuracy (e.g., the North American Coordinate System, 1983-NAD83- only suitable for use in the United States, but not in Europe). Projection is an essential part of making maps. It is a mathematical method of converting information from a model of the Earth by converting a curved three-dimensional surface into a two-dimensional medium (such as paper or a computer screen). Different types of maps use different projection systems, because each projection system has its own appropriate use. A projection that accurately reflects the shape of continents, for example, would distort their relative sizes.
Spatial analysis
Spatial analysis ability is the main function of GIS and also the main feature that distinguishes GIS from computer mapping software. Spatial analysis is to study spatial things from the aspects of spatial position and connection of spatial objects, and to make quantitative description of spatial things. Spatial analysis needs complex mathematical tools, among which the most important are spatial statistics, graph theory, topology and calculation of geometric geometry. Its main task is to describe and analyze spatial structure, so as to obtain, describe and recognize spatial data. The background process of understanding and interpreting geographical patterns; Simulation and prediction of spatial processes; To regulate events that occur in geographical space.