What's the use of learning GIS?

Geographic Information System (GIS) deals with and manages all kinds of geospatial entity data and their relationships, including spatial positioning data, graphic data, remote sensing image data, attribute data and so on. It is used to analyze and deal with various phenomena and processes distributed in a certain geographical area, and to solve complex planning, decision-making and management problems.

Through the above analysis and definition, we can put forward the following basic concepts of GIS:

1, the physical shell of geographic information system is a computerized technical system, which consists of several interrelated subsystems, such as data acquisition subsystem, data management subsystem, data processing and analysis subsystem, image processing subsystem and data product output subsystem. The quality and structure of these subsystems directly affect the hardware platform, function, efficiency, data processing mode and product output type of GIS.

2. The operation object of 2.GIS is spatial data, that is, geographical entities with three-dimensional elements such as points, lines, surfaces and bodies. The most fundamental feature of spatial data is that each data is coded according to unified geographical coordinates, which realizes its positioning, qualitative and quantitative description. This is the fundamental sign that GIS is different from other types of information systems, and it is also a technical difficulty.

3. The technical advantage of 3.GIS lies in its ability of data synthesis, simulation, analysis and evaluation, which can obtain important information that is difficult to obtain by conventional methods or ordinary information systems, and realize the simulation and prediction of geospatial process evolution.

4.GIS is closely related to surveying and geography. Geodetic survey, engineering survey, mine survey, cadastral survey, aerial photogrammetry and remote sensing technology provide various positioning numbers with different scales and different accuracy for spatial entities in GIS; The use of modern surveying and mapping technologies, such as electronic speedometer, GPS global positioning technology, analytic or digital photogrammetry workstation and remote sensing image processing system, can directly, quickly and automatically obtain digital information products of space targets, provide rich and more real-time information sources for GIS, and promote the development of GIS to a higher level. Geography is the theoretical support of geographic information system.

Some scholars assert that "geographic information system and information geography are the main tools and means of the second revolution of geographical science." If the rise and development of GIS is a key to the information revolution of geographical science, then the rise and development of information geography will be a door to the information revolution of geographical science and will certainly open up a brand-new world for the development and perfection of geographical science. "GIS is called the third generation language of earth science-describing spatial entities in digital form. Classification of geographic information systems According to the research scope, geographic information systems can be divided into global, regional and local. According to the different research contents, it can be divided into comprehensive and thematic. Various professional application systems at the same level can form a regional integrated system at the same level in the corresponding area. When planning and establishing application systems, it is necessary to plan the development of these two systems in a unified way, so as to reduce repeated waste and improve the appreciation and practicability of data. Extension: Distribution Geographic Information System Geographic Information System (GIS) is an important part of distribution automation system: because there are many nodes and scattered equipment in distribution network, its operation and management work is often related to geographical location, and the introduction of distribution geographic information system can make operation and management more intuitive; Its contents mainly include: equipment management (FM), which reflects the technical data of substations, feeders, transformers, switches, poles and other equipment on the geographical background map; Customer Information System (CIS) refers to the processing of a large number of user information, such as user name, address, account number, telephone number, power consumption and load, power supply priority, power outage records, etc. With the help of GIS, it is convenient to quickly judge the influence range of the fault, and the statistical information of electricity consumption and load can also be used as the basis for network analysis; Power outage management system (OMS) means that after GIS receives power outage complaints, by calling CIS and SCADA functions, it can quickly find out the fault location and influence range, select a reasonable operation sequence and path, display the progress in the processing process, and automatically transmit relevant information to the user complaint telephone answering system; In addition, GIS can also have the function of assisting distribution network development planning and design. The development of China's geographic information system started late, but the development momentum is quite rapid, which can be roughly divided into the following three stages.

The first is the initial stage. In the early 1970s, China began to popularize the application of electronic computers in the fields of surveying, mapping and remote sensing. With the development of international remote sensing technology, China began to introduce American earth resources satellite images in 1974 to carry out remote sensing image processing and interpretation. 1976 held the first remote sensing technology planning meeting, which formed a new situation of vigorous development of remote sensing technology experiments and applications, and successively carried out infrared remote sensing experiments in Beijing, Tianjin and Tangshan areas. Xinjiang Hami aerial remote sensing experiment, Tianjin Bohai Bay environmental remote sensing research, Tianjin agricultural land resources remote sensing inventory. For a long time, the State Bureau of Surveying and Mapping has systematically carried out a series of aerial photogrammetry and topographic mapping, which laid a solid foundation for the establishment of GIS database. The research and application of analytical mapping and digital mapping, computer-aided mapping and digital elevation model are also carried out simultaneously. 1977, the first all-factor map output by computer was born. 1978, the State Planning Commission held the first national database forum in Huangshan. All these have made technical preparations for the development and application of geographic information system.

The second is the experimental stage. After entering the 1980s, China implemented the "Sixth Five-Year Plan" and the "Seventh Five-Year Plan", and the national economy developed in an all-round way, which quickly made a warm response to the "information revolution". While vigorously developing the application of remote sensing, GIS has also entered the experimental stage. In the typical experiment, the data specification and standard, the construction of spatial database, the algorithm of data processing and analysis and the development of application software are mainly studied. Taking agriculture as the object, this paper studies the model and software of quality evaluation and dynamic analysis and prediction, and applies it to the experimental research of reservoir inundation loss, water resources estimation, land resources inventory, environmental quality evaluation and population trend analysis. In terms of thematic experiments and applications, on the basis of national geodesy and establishment of digital ground model, the national 1: 1 10,000 land database system, national land information system, national1:400,000 resource and environment information system and1:2.5 million soil and water conservation information system have been established, and the information system of loess plateau and the flood disaster prediction and analysis system have been developed. Various small information systems used to assist urban planning have also been recognized by urban construction and planning departments.

Great progress has been made in academic exchanges and personnel training. Many international academic seminars on GIS were held in China. 1985 China academy of sciences established the state key open laboratory of resources and environmental information system, 1988 and 1990 Wuhan surveying and mapping university successively established the state key open laboratories of information engineering and surveying and mapping remote sensing information engineering. Many universities in China have set up remote sensing courses and workshops at different levels, and trained a large number of doctors and masters engaged in the research and application of geographic information systems.

The third is the all-round development stage of GIS. Since the late 1980s and 1990s, with the development of socialist market economy, China's geographic information system has entered an all-round development stage. The State Bureau of Surveying and Mapping is establishing a digital surveying and mapping information industry nationwide. 1: 1 10,000 map database has been put on sale, Wei: 250,000 map database has also been built, and the production and construction of national 1: 1 10,000 map database has been started. The Provincial Bureau of Surveying and Mapping is working hard to establish a provincial-level basic geographic information system of 1: 1 10,000. The application of digital photogrammetry and remote sensing has gradually shifted from typical experiments to operational systems, which can ensure the continuous provision of topographic and thematic information to geographic information systems. Since 1990s, the development of coastal and riverside economic development zones, the paid use of land and the introduction of foreign capital all urgently need GIS services, which has effectively promoted the development of urban geographic information system. Many cities in China have established urban information systems for urban planning, land management, transportation, electricity and various infrastructure management.

In terms of basic research and software development, the Ministry of Science and Technology included "the comprehensive application of remote sensing, geographic information system and global positioning system" in the Ninth Five-Year Plan, and invested considerable research funds in this project to support Wuhan Technical University of Surveying and Mapping, Peking University, China Geo University, China Academy of Forestry and Institute of Geography of China Academy of Sciences to develop basic GIS software with independent copyright in China. After several years of hard work, the gap between China's GIS basic software and foreign countries has narrowed rapidly, and a number of GIS software such as GeoStar, MapGIS, OityStar and ViewGIS have emerged. In remote sensing, with the support of this project, a national land dynamic monitoring information system based on the land classification results of IK4 remote sensing images was established. The implementation of this major national project has greatly promoted the development of remote sensing and geographic information system in China. Experts at home and abroad have different definitions of GIS (some foreign definitions of GIS are taken from David J. Maguire, 199 1).

1、DoE( 1987: 132)

A system for capturing, storing, checking, processing, analyzing and displaying geospatial reference data.

2. Aaronov (1989:39)

Any manual or computer-based assembly used to store and manipulate geo-referenced data.

3. Carter (1989:3)

An organization as a whole reflects an organizational structure, which combines technology with databases, professional knowledge and continuous financial support.

4. Parker (1988: 1547)

An information technology for storing, analyzing and displaying spatial and non-spatial data.

5. Duke (1979: 106)

A special case of an information system in which the database consists of observations of spatially distributed features, activities or events, which can be defined as points, lines or surfaces in space. GIS processes data about these points, lines and regions to retrieve data for special query and analysis.

6. Smith et al. (1987: 13)

A database system in which most data are indexed by space, and on this basis, a set of procedures are run to answer queries about spatial entities in the database.

7. Ozemoy, Smith and Szicher Mann (198 1:92)

A set of automation functions that provide professionals with advanced functions of storing, retrieving, manipulating and displaying geographic location data.

8. Bale (1986:6)

A powerful tool for collecting, storing, randomly retrieving, transforming and displaying real-world spatial data.

9. Cowen (1988: 1544)

A decision support system relates to the integration of spatial reference data in a problem-solving environment.

10, Kosca lev, ti Kunov and Trofimov (1989:256)

A system with advanced geological modeling capability.

1 1, Devine and Field( 1986: 18)

A form of MIS[ that allows map display of general information.

12, Chen et al. (1999, introduction to information systems):

It consists of computer system, geographic data and users. Through the integration, storage, retrieval, operation and analysis of geographic data, it generates and outputs all kinds of geographic information, thus providing new knowledge for government departments in land use, resource management, environmental monitoring, transportation, economic construction, urban planning and administrative management, and serving for engineering design, planning and management decisions. Engineering is cartography and geographic information engineering, which belongs to surveying and mapping and focuses on measurement. There is no essential difference between the two. According to their own preferences, engineering is generally set up in science and engineering colleges, and science is generally set up in comprehensive universities or normal universities. In science, the geographic information system of the School of Resources and Environmental Sciences of Wuhan University is quite powerful, especially in cartography. The development background of GIS 35,000 years ago, French Krumanon hunters drew the patterns of the animals they hunted on the cave wall near Lascaux. Related to these animal pictures are some lines and symbols that describe the migration route and trajectory. These early records conform to the dual structure of modern geographic information system: one graphic file corresponds to one attribute database. The modern surveying technology of18th century topographic map has been realized, and at the same time, early versions of thematic mapping, such as scientific aspects or census data, have appeared. At the beginning of the 20th century, the "lithography" of layering pictures was developed. Until the early 1960s, with the advancement of nuclear weapons research, the development of computer hardware led to the application of general computer "drawing".

1967 The world's first practical GIS system was developed by the Federal Department of Energy, Mines and Resources in Ottawa, Ontario. Developed by roger Tomlinson, the system is called "Canadian Geographic Information System" (CGIS). It is used to store, analyze and process the collected data about the Canadian Land Survey (CLI). CLI measures the land capacity of rural Canada by plotting all kinds of information about soil, agriculture, leisure, wildlife, waterfowl, forestry and land use at the ratio of1:250,000, and adds the rank classification factor for analysis.

CGIS is the first "system" in the world, and it has been improved in the application of "drawing". It has the functions of covering, measuring and digitizing/scanning data, supports transcontinental country coordinate system, encodes lines into "arcs" with real embedded topological structure, and stores the information of attributes and positions in separate files. Roger Tomlinson, its developer and geographer, is called "the father of geographic information system".

CGIS was not completed until 1970s, but it took a long time, so in its initial development period, it could not compete with vendors selling various commercial map applications, such as Graph. With the development of microcomputer hardware, manufacturers such as ESRI and karis have successfully merged most CGIS features, and combined the 1 generation method for separating spatial and attribute information with the second generation method for organizing attribute data into database structure. The industrial growth in 1980s and 1990s stimulated the rapid growth of UNIX workstations and personal computers using GIS. By the end of the 20th century, the rapid growth of various systems made it consolidated and standardized in a few related platforms. And users began to put forward the concept of viewing GIS data on the Internet, which requires the standardization of data format and transmission. The technology used in GIS obtains relevant information from different sources.

If you can relate the rainfall in your state to the photos of your county, you can determine which wetland will dry up at some time of the year. Geographic information system can do this kind of analysis, and it can apply information from different sources in different forms. The basic requirement for source data is to determine the location of variables. Location can be marked by X, Y and Z coordinates of longitude, latitude and altitude, or represented by other geocoding systems, such as postal codes or highway mileage signs. Any variable that can be located and stored can be fed back to GIS. Some government agencies and non-governmental organizations are making computer databases that can directly access GIS. You can import different types of data formats in the map into GIS. At the same time, GIS system can convert digital information in non-map form into a form that can be recognized and used. For example, by analyzing the digital satellite images generated by remote sensing, a digital information layer about vegetation cover similar to a map can be generated. Similarly, the data of population survey or hydrological table can also be converted into the form of map as the subject information layer in GIS system.

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GIS data represents the objective objects (roads, land use, altitude) in the real world in the form of digital data. The objective objects in the real world can be divided into two abstract concepts: discrete objects (such as houses) and continuous object areas (such as rainfall or altitude). There are two main methods to store data in GIS: grid and vector. Grid data consists of rows and columns that hold unique value storage units. It is similar to a grid image. In addition to using appropriate colors, the value recorded by each unit can also be a classification group, such as land use, continuous value or rainfall, or a null value recorded when the data is not available. The resolution of raster datasets depends on the grid width of ground units. Usually, the storage unit represents a square area of the ground, but it can also be used to represent other shapes. Raster data can be used to represent areas or objects, and vector data stored as ... uses geometric figures such as points, lines (a series of point coordinates) or faces (the shape depends on lines) to represent objective objects. For example, housing subdivision, using polygons to represent the boundary of real estate, and using points to accurately represent the location. Vectors can also be used to represent fields with continuous variability. Use contour lines and TIN to represent altitude or other changing values. The records of TIN evaluate these points connected into an irregular grid composed of triangles. The face of a triangle represents the terrain surface. It has advantages and disadvantages to express reality with raster or vector data model. Raster data is set to have the same value at all points in the recording plane, while vector format only stores data where needed, which makes the former need more storage space than the latter. It is easy to overwrite raster data, but it is much more difficult for vector data. Vector data can be displayed like vector graphics on a traditional map, but when raster data is displayed as an image, the boundary of the display object will be blurred. In addition to the spatial data expressed by geometric vector coordinates or grid cell positions, other non-spatial data can be stored. In vector data, these additional data are attributes of objective objects. For example, a polygon of forest resources may contain identifier values and information about tree species. Cell values in raster data can store attribute information, but they can also be used as identifiers related to records in other tables.

Information retrieval

Data retrieval-inputting data into the system-takes up most of the time of GIS practitioners. There are many ways to input data into GIS, among which data is stored in digital format. Existing data printed on paper or polyester film maps can be digitized or scanned to generate digital data. The digitizer generates vector data from the map as the boundary of the operator's trajectory points, lines and polygons. Scanning a map can generate raster data, which can be further processed to generate vector data. The measurement data can be directly input into GIS from the digital data acquisition system on the measuring instrument. The position obtained from another measuring tool, Global Positioning System (GPS), can also be directly input into GIS. Remote sensing data also plays an important role in data collection, which consists of multiple sensors attached to the platform. Sensors include cameras, digital scanners and lidar, while platforms usually consist of airplanes and satellites. At present, most digital data comes from photo interpretation and aerial photos. Soft copy workstation is used to digitize features directly obtained from stereo image pairs of digital images. These systems allow data to be acquired in two or three dimensions, and their heights can be measured directly from stereo image pairs based on photogrammetry. At present, analog aerial photos are scanned before being input into the soft copy system, but this step can be omitted as high-quality digital cameras become cheaper and cheaper. Satellite remote sensing provides another important source of spatial data. Here, the satellite uses different sensor packages to passively measure the electromagnetic wave spectrum or the reflection coefficient of some radio waves emitted by active sensors such as radar. Remote sensing data can be further processed to identify objects and categories of interest, such as raster data of land cover. In addition to collecting and inputting spatial data, attribute data should also be input into GIS. For vector data, this includes additional information about the objects represented in the system. After data is input into GIS, it is usually edited to eliminate errors or further processing. For some advanced analysis, vector data must be "topologically correct". For example, in a road network, lines must be connected with nodes at intersections. Errors such as backlash or overshoot must also be eliminated. For scanned maps, it may be necessary to remove stains from the source map from the generated raster. For example, a dirt spot may connect two lines that should not be connected.

data manipulation

GIS can reconstruct data and convert data into different formats. For example, GIS can convert satellite images into vector structures by generating lines around all units with the same classification and determining the spatial relationships of the units, such as adjacency and inclusion.

Because digital data is collected and stored in different ways, the two data sources may not be completely compatible. Therefore, GIS must be able to transform geographic data from one structure to another.

Projection system, coordinate system and transformation

Property ownership map and soil distribution map may display data at different scales. Map data in GIS must be manipulated to be consistent with or cooperate with data obtained from other maps. Before analyzing digital data, they may need to go through other processes to integrate into GIS, such as projection and coordinate transformation. The earth can be represented by many models. For any given point on the earth's surface, each model may give a different set of coordinates (such as latitude, longitude and altitude). The simplest model is to assume that the earth is an ideal sphere. With the gradual accumulation of geodetic data, the earth model becomes more and more complex and accurate. In fact, some models are applied to different regions of the earth to provide higher accuracy (such as North American coordinate system, 1983-NAD83- only applicable to the United States, not to Europe).

Projection is the basic part of making maps. This is a mathematical method to convert information from the earth model. It transforms a three-dimensional surface into a two-dimensional medium (such as paper or computer screen). Different types of maps should use different projection systems, because each projection system has its own suitable purpose. For example, a projection that can accurately reflect the shape of a continent will distort its relative size.

GIS spatial analysis

Spatial analysis ability is the main function of GIS, and it is also the main feature that distinguishes GIS from computer drawing software. Spatial analysis is to study and quantitatively describe spatial things from the aspects of spatial position and connection of spatial objects. Generally speaking, only answer what (what is it? ), where (where? How's it going? ) and other questions, not (can) answer why (why? )。 Spatial analysis needs complex mathematical tools, among which the most important ones are spatial statistics, graph theory, topology, computational geometry and so on. [1]. Its main task is to describe and analyze spatial composition in order to obtain, describe and identify spatial data. The background process of understanding and explaining geographical patterns; Simulation and prediction of spatial processes; The purpose of adjusting events in geographical space [2].

Spatial analysis technology involves many disciplines, and professional disciplines such as geography, economics, regional science, atmosphere, geophysics and hydrology provide knowledge and mechanism for it.

In addition to the spatial analysis module bundled with GIS software, there are also some special spatial analysis software, such as GISLIB, SIM, PPA, Fragstats and so on.

data modeling

It is difficult to connect the wetland map with the rainfall recorded in different places such as airports, TV stations and schools. However, GIS can describe the two-dimensional and three-dimensional characteristics of the surface, underground and atmosphere.

For example, GIS can quickly draw a rainfall line that reflects rainfall.

Such a map is called a rainfall map. The characteristics of the whole surface can be estimated by measuring a limited number of points, which is very mature. In GIS, two-dimensional rainfall map can be superimposed and analyzed with other layers in the same area.

Topological modeling

Have there been any gas stations or factories near the wetland in the past 35 years? Is there such a facility to meet the requirement of being within 2 miles above the wetland? GIS can identify and analyze this spatial relationship in digital spatial data. These topological relationships allow complex spatial modeling and analysis. The topological relations of geographical entity sound include connection (what is connected with what), inclusion (what is in what) and proximity (the distance between them).

Network modeling

If all factories near the wetland discharge chemicals into the river at the same time, how long will it take for the amount of pollutants discharged into the wetland to reach the amount that damages the environment? GIS can simulate the diffusion path of pollutants along linear networks (rivers). Numerical values such as slope, speed limit and pipe diameter can be incorporated into the model to make the simulation more accurate. Network modeling is usually used in traffic planning, hydrological modeling and underground pipe network modeling.