The objects processed and managed by the geographic information system are a variety of geographical spatial entity data and their relationships, including spatial positioning data, graphic data, remote sensing image data, attribute data, etc., which are used to analyze and process information in a certain geographical area. Various phenomena and processes distributed within the region to solve complex planning, decision-making and management problems.
Through the above analysis and definition, the following basic concepts of GIS can be put forward:
1. The physical shell of GIS is a computerized technical system, which is composed of several interrelated sub-systems. System components, such as data collection subsystem, data management subsystem, data processing and analysis subsystem, image processing subsystem, data product output subsystem, etc. The quality and structure of these subsystems directly affect the hardware platform and functions of GIS. , efficiency, method of data processing and type of product output.
2. The operation object of 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 encoded according to unified geographical coordinates to achieve 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 its technical difficulty.
3. The technical advantage of GIS lies in its data synthesis, simulation and analysis and evaluation capabilities. It can obtain important information that is difficult to obtain by conventional methods or ordinary information systems, and realize the simulation and prediction of the evolution of geospatial processes.
4. GIS is closely related to surveying and geography. Geodesy, engineering survey, mine survey, cadastral survey, aerial photogrammetry and remote sensing technology provide positioning data of various scales and accuracy for spatial entities in GIS; electronic speedometer, GPS global positioning technology, analytical or digital photogrammetry The use of modern surveying and mapping technologies such as workstations and remote sensing image processing systems can directly, quickly and automatically obtain digital information products of spatial targets, provide GIS with rich and more real-time information sources, and promote the development of GIS to a higher level. Geography is the theoretical basis of GIS.
Some scholars assert that “geographic information systems and information geography are the main tools and means of the second revolution in geographical science. If the rise and development of GIS are a key to the information revolution in geographical science, Then, the rise and development of information geography will be a door to the information revolution in geographical science and will definitely open up a new world for the development and improvement of geographical science." GIS is known as the third generation language of geoscience - using digital form to describe spatial entities. Classification of Geographic Information Systems (GIS) GIS can be divided into global, regional and local according to the scope of research; it can be divided into comprehensive and thematic according to different research contents. Various professional application systems at the same level can be gathered together to form a regional comprehensive system at the same level in the corresponding region. When planning and establishing application systems, the development of these two systems should be planned uniformly to reduce duplication and waste and improve data sharing and practicality. Extension: Distribution Geographic Information System Geographic Information System (GIS) is an important part of the distribution automation system: Since the distribution network has many nodes and scattered equipment, its operation and management work is often related to geographical location, so the distribution Geographic Information System is introduced , which allows for more intuitive operation management; 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; User Information System (CIS) , refers to using GIS to process a large amount of user information, such as user name, address, account number, phone number, power consumption and load, power supply priority, power outage records, etc., so as to quickly determine the scope of impact of the fault, and the power consumption and load Statistical information can also be used as the basis for network analysis; the power outage management system (OMS) refers to the GIS that calls the CIS and SCADA functions to quickly identify the fault location and scope of impact after receiving a power outage complaint, and selects a reasonable operation sequence and path. Display the progress in the processing process and automatically transfer relevant information to the user complaint telephone response system; in addition, GIS can also have the function of assisting distribution network development planning and design.
The development of geographical information system in my country my country’s geographical information system started a little late, but its development momentum is quite rapid and can be roughly divided into the following three stages.
The first is the initial stage. In the early 1970s, my country began to promote the application of electronic computers in the fields of measurement, mapping and remote sensing. With the development of international remote sensing technology, my country began to introduce U.S. Earth Resources satellite images in 1974 and carried out remote sensing image processing and interpretation. The first remote sensing technology planning meeting was held in 1976, forming a new situation of vigorous development of remote sensing technology experiments and applications. Infrared remote sensing experiments were carried out in Beijing, Tianjin and Tangshan. Aerial remote sensing experiments in the Hami region of Xinjiang, environmental remote sensing research in the Bohai Bay region of Tianjin, and remote sensing inventory of agricultural land resources in the Tianjin region. For a long time, the State Bureau of Surveying and Mapping has systematically carried out a series of aerial photogrammetry and topographic mapping, laying a solid foundation for the establishment of a geographic information system database. The research and use of analytical and digital mapping, machine-assisted mapping, and digital elevation models are also carried out simultaneously. In 1977, the first full-element map output by computer was produced. In 1978, the State Planning Commission held the first national database academic symposium in Huangshan. All these have made technical preparations for the development and application of GIS.
The second is the experimental stage. After entering the 1980s, our country implemented the "Sixth Five-Year Plan" and the "Seventh Five-Year Plan", and the national economy developed in an all-round way, and soon responded enthusiastically to the "information revolution". While vigorously developing remote sensing applications, GIS has also entered the experimental stage. In typical experiments, data specifications and standards, spatial database construction, data processing and analysis algorithms and application software development are mainly studied. Focusing on agriculture, we study models and software related to quality evaluation and dynamic analysis and forecasting, and use them for experimental research on many topics such as reservoir inundation loss, water resource estimation, land resource inventory, environmental quality evaluation, and population trend analysis. In terms of special experiments and applications, based on the establishment of national geodetic surveys and digital ground models, a national 1:1 million land retention database system and a national land information system, a 1:4 million national resource and environmental information system and a 1:4 million national resource and environmental information system have been built. : 2.5 million soil and water conservation information system, and carried out special research experiments such as the Loess Plateau information system and the flood disaster forecast and analysis system. Various small information systems used to assist urban planning have also gained recognition in urban construction and planning departments.
Great development has been achieved in academic exchanges and talent cultivation. Many international academic seminars on GIS have been held in China. In 1985, the Chinese Academy of Sciences established the "National Key Open Laboratory of Resource and Environmental Information Systems". In 1988 and 1990, Wuhan University of Science and Technology of Surveying and Mapping established the "Information Engineering Major" and the "National Key Open Laboratory of Surveying, Mapping and Remote Sensing Information Engineering". ". Many universities in our country have opened RS courses and workshops at different levels, and have trained a large number of PhDs and masters in GIS research and application.
The third is the comprehensive development stage of GIS. From the late 1980s to the 1990s, my country's GIS entered a stage of comprehensive development with the development of the socialist market economy. The State Bureau of Surveying and Mapping is establishing a nationwide digital surveying and mapping information industry. The 1:1,000,000 map database has been put on public sale, and the W:250,000 map database has also been completed. The production and construction of the national 1:100,000 map database has begun. The provincial surveying and mapping bureaus are working hard to establish provincial-level 1:10,000 map databases. Basic GIS. Digital photogrammetry and remote sensing applications are gradually moving from typical experiments to operational systems, which can ensure a continuous supply of terrain and thematic information to GIS. Since the 1990s, the development of coastal and riverside economic development zones, the paid use of land and the introduction of foreign capital have urgently required GIS services, which has effectively promoted the development of urban geographic information systems. Urban information systems used for urban planning, land management, transportation, electricity and various infrastructure management have been established in many cities in my country.
In terms of basic research and software development, the Ministry of Science and Technology has included "the comprehensive application of remote sensing, geographical information systems and global positioning systems" in the "Ninth Five-Year Plan" scientific and technological research plan as an important national "Ninth Five-Year Plan" Zhongzhi Science and Technology Research Project, in which a considerable amount of research funds are invested to support Wuhan University of Surveying and Mapping Technology, Peking University, China University of Geosciences, Chinese Academy of Forestry Sciences, Institute of Geography, Chinese Academy of Sciences and other units to develop my country's independent copyright geographical information System basic software. After several years of hard work, the gap between China's GIS basic software and foreign countries has rapidly narrowed, and several geographic information system software that can participate in market competition have emerged, such as GeoStar, MapGIS, OityStar, ViewGIS, etc. In terms of 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 has been established. The implementation of this major national project has effectively promoted the development of remote sensing and geographic information systems in China. Domestic and foreign experts have different definitions of geographic information systems (some foreign definitions of geographic information systems are taken from David J. Maguire, 1991).
1. DoE (1987: 132)
a system for capturing storing checking, manipulating analyzing and displaying data which are spatially referenced the Earth.
2. Aronoff (1989: 39)
Any manual or computer based set of procedures used to store and manipulate geographically referenced data.
3. Carter (1989: 3)
an institutional entiry, reflecting an organizational structure that integrates technology with a database, expertise and continuing, financial support over time.
4. Parker (1988: 1547)
an information technology which stores, analyzes, and displays both spatial and non-spatial data.
5. Dueker (1979: 106)
a special case of information systems where the database consists of observations on spatioally distributed features, activities, or events, which are definable in space as points, lines, or areas. A GIS manipulates data about these points, lines, and areas to retrieve data for ad hoc queries and analysis.
6. Smith et al. (1987: 13)
a database system in which most of the data are spatially indexed, and upon which a set of procedures operated in order to answer queries about spatial entities in the database.
7. Ozemoy, Smith and Sicherman (1981: 92)
an automated set of functions that provides professionals with advanced capabilities for the storage, retrieval, manipulation, and display of geographically located data.
8.B
urrough (1986: 6)
a powerful set of tools for collecting, storing, retrieving at will, transforming and displaying spatial data from the real world.
9. Cowen (1988: 1544)
a decision support system involving the integration of spatially referenced data in a problem-soling environment.
10. Koshkariov, Tikunov and Trofimov (1989: 256)
a system with advanced geo-modelling capabilites.
11. Devine and Field (1986: 18)
a form of MIS[Management Informaion System]that allows map display of the general information.
12. Statement Peng et al. (1999, "Introduction to Geographic Information Systems"):
It is composed of computer systems, geographic data and users. Through the integration of geographic data , store, retrieve, operate and analyze, generate and output various geographical information, thereby providing new knowledge for land use, resource management, environmental monitoring, transportation, economic construction, urban planning and government department administrative management, and providing engineering design and Planning, management and decision-making services. Some things to note when registering for the GIS major in the college entrance examination. Currently, there are many colleges offering geographic information system majors. However, when registering for the college entrance examination, please note that cartography and geographic information systems are divided into science subjects, which belong to geography and focus on the application of geography. Theoretical research; the engineering major is cartography and geographical information engineering, which belongs to surveying and mapping, focusing on measurement. There is no essential difference between the two. When applying, you can choose based on your own preferences. Engineering majors are generally offered in science and engineering colleges, while science majors are generally offered in comprehensive universities or normal universities. As for science, the geographical information system of the School of Resources and Environmental Sciences of Wuhan University is quite good, especially in the field of cartography. Background on the development of GIS 35,000 years ago, French Cro Magnon hunters painted images of the animals they hunted on cave walls near Lascaux. Associated with these animal drawings are lines and symbols describing migration routes and trajectories. These early records conformed to the two-element structure of modern geographic information systems: a graphics file corresponding to an attribute database. The 18th century saw the advent of modern surveying techniques for topographic mapping, as well as early versions of thematic mapping, for example scientific or household census data. In the early 20th century, "photolithography", which divided pictures into layers, was developed. Until the early 1960s, the development of computer hardware, driven by nuclear weapons research, led to the application of general-purpose computer "drawing".
The world's first operational GIS system was developed in Ottawa, Ontario, in 1967 by the federal Department of Energy, Minerals and Resources. This system was developed by Roger Tomlinson and is called "Canadian GIS" (CGIS). It is used to store, analyze and process data collected from the Canadian Land Inventory (CLI). CLI measures land capacity for rural Canada by mapping a variety of information on soils, agriculture, recreation, wildlife, waterfowl, forestry, and land use at a scale of 1:250,000, and adds hierarchical classification factors for analysis. .
CGIS is the world's first "system" and improves on the "mapping" application. It has the functions of covering, surveying, data digitization/scanning, and supports a cross-continental national coordinate system. , lines are encoded as “arcs” with true embedded topology, and information about attributes and positions are stored in separate files. Its developer, geographer Roger Tomlinson, is known as the "Father of GIS."
CGIS was not completed until the 1970s, but this took too long to compete with commercial map application software vendors such as Intergraph in its early stages of development. business competition. Developments in microcomputer hardware have allowed vendors such as ESRI and CARIS to successfully incorporate most CGIS features and combine the first-generation approach to the separation of spatial and attribute information with the second-generation approach to organizational attribute data. Generation method into database structure. Industrial growth in the 1980s and 1990s spurred the rapid growth of UNIX workstations and personal computers using GIS. By the end of the 20th century, its rapid growth in various systems had led to its consolidation and standardization on a small number of relevant platforms. And users began to propose the concept of viewing GIS data on the Internet, which requires standardization of data format and transmission. The techniques used in GIS derive relevant information from different sources
If you could correlate rainfall in your state with photos from the skies above your county, you could tell which wetlands were wet at certain times of the year. dry up. A GIS system can perform such 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. Locations may be represented by x, y, and z coordinates of longitude, latitude, and altitude, or by other geocoding systems such as ZIP codes, or highway mile markers. Any variable that can be located and stored can be fed back to GIS. Several government agencies and non-governmental organizations are producing computer databases that can directly access GIS. Different types of data formats from maps can be imported into GIS. GIS systems can also convert digital information that is not in map form into a recognizable and usable form. For example, by analyzing digital satellite images generated by remote sensing, a map-like layer of digital information about vegetation cover can be generated. Likewise, census or hydrographic tabular data can be converted into map form as a thematic information layer in a GIS system.
Data presentation
GIS data represents real-world objective objects (roads, land use, altitude) in the form of digital data. Real-world objective objects can be divided into two abstract concepts: discrete objects (such as houses) and continuous object fields (such as rainfall or altitude). The two main methods for storing data in GIS systems are: raster (grid) and vector. Raster (grid) data consists of rows and columns that hold unique value storage cells. It is similar to a raster (grid) image. In addition to using appropriate colors, the value recorded in each unit may also be a classification group, such as land use status, a continuous value, or rainfall, or A null value logged when data is not available. The resolution of the raster dataset depends on the grid width of the ground units. Typically the memory cells represent square areas of the ground, but can be used to represent other shapes. Raster data can be used to represent either an area or a physical object, which is stored as... Vector data utilizes geometric figures such as points, lines (a series of point coordinates), or surfaces (shapes determined by line) to represent objective objects. For example, in a housing subdivision, polygons are used to represent property boundaries and points are used to accurately represent locations. Vectors can also be used to represent areas of continuous variability. Contours and triangulated irregular networks (TINs) are used to represent elevation or other continuously changing values. TIN records are evaluated against points connected into an irregular grid of triangles. The face on which the triangle lies represents the terrain surface.
There are advantages and disadvantages to utilizing raster or vector data models to represent reality. Raster data is set to record the same value at all points in the plane, while vector format only stores data where needed, which makes the former require more storage space than the latter. The overlay operation can be easily implemented for raster data, but it is much more difficult for vector data. Vector data can be displayed like vector graphics on a traditional map, while raster data will have blurred boundaries when displayed as an image. In addition to spatial data expressed in geometric vector coordinates or raster cell positions, other non-spatial data can also be stored. In vector data, these additional data are attributes of the objective object. For example, a forest resource polygon might contain an identifier value and information about the tree species. Cell values ??in raster data can store attribute information, but can also serve as identifiers related to records in other tables.
Data retrieval
Data retrieval - inputting data into the system - occupies most of the time of GIS practitioners. There are several ways to enter data into a GIS where it is stored in a numerical format. Existing data printed on paper or Mylar maps can be digitized or scanned to produce digital data. The digitizer generates vector data from the map as operator trajectory points, lines, and polygon boundaries. Scanning the map can produce raster data that can be further processed to generate vector data. Measurement data can be entered directly into the GIS from the digital data collection system on the measuring instrument. Locations obtained from the Global Positioning System (GPS), another measurement tool, can also be entered directly into a GIS. Remote sensing data also plays an important role in data collection and consists of multiple sensors attached to the platform. Sensors include cameras, digital scanners and lidar, while platforms typically consist of aircraft and satellites. Most digital data now comes from image interpretation and aerial photographs. The soft copy workstation is used to digitize features obtained directly from stereo pairs of digital images. These systems allow data to be captured in two or three dimensions, with their elevations measured directly from stereoscopic pairs using photogrammetric principles. Today, analog aerial photos are scanned and then fed into soft-copy systems, but as high-quality digital cameras become more affordable, this step can be omitted. Satellite remote sensing provides another important source of spatial data. Here satellites use different sensor packages to passively measure the reflection coefficient of the portion of the electromagnetic spectrum or radio waves emitted from active sensors such as radar. Remote sensing collections can be further processed to identify objects and classes of interest such as land cover in raster data. In addition to collecting and entering spatial data, attribute data is also entered into the 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 for further processing. Vector data must be "topologically correct" to perform some advanced analyses. For example, in a road network, lines must connect to nodes at intersections. Errors like kickback or overshoot must also be eliminated. For scanned maps, stains on the source map may need to be eliminated from the resulting raster. For example, specks of dirt may connect two lines together that shouldn't be connected.
Data operations
GIS can perform data reconstruction to convert data into different formats. For example, GIS can convert satellite images into vector structures by generating lines around all cells with the same classification while determining the spatial relationships of cells, such as adjacency and inclusion.
Because digital data is collected and stored in different ways, the two data sources may not be fully compatible. Therefore GIS must be able to transform geographic data from one structure to another.
Projection Systems, Coordinate Systems and Transformations
Property ownership maps and soil distribution maps may display data at different scales. Map data in a GIS must be manipulated to align or fit with data obtained from other maps. Before digital data can be analyzed, they may undergo other processing to integrate them into a GIS, such as projection and coordinate transformation.
The Earth can be represented by a variety of models, and each model may give a different set of coordinates (such as latitude, longitude, altitude) 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 are accumulated, models of the Earth become more complex and more precise. In fact, some models are applied to different regions of the Earth to provide greater accuracy (such as the North American Coordinate System, 1983 - NAD83 - only suitable for use in the United States, not in Europe).
Projection is a fundamental part of map making. It is a mathematical method of converting information from a model of the Earth. It converts a three-dimensional curved surface into a two-dimensional medium (such as paper or a computer screen). Different types of maps require different projection systems, as each projection system has its own appropriate uses. For example, a projection that accurately reflects the shape of a continent would distort the relative size of the continents (translated from English Wikipedia)
GIS Spatial Analysis
Spatial analysis capabilities are the primary function of GIS , which is also the main feature that distinguishes GIS from computer mapping software. Spatial analysis is to study spatial things from the spatial position and connection of spatial objects, and to make quantitative descriptions of spatial things. Generally speaking, it only answers questions such as What (what?), Where (where?), How (how?), etc., but it does not (can) answer Why (why?). Spatial analysis requires complex mathematical tools, the most important of which are spatial statistics, graph theory, topology, computational geometry, etc. [1]. Its main task is to describe and analyze the composition of space to achieve acquisition, description and cognition. Spatial data; understanding and explaining the background process of geographical patterns; simulation and prediction of spatial processes; regulating events that occur in geographical space, etc. [2].
Spatial analysis technology is related to many disciplines, and specialized disciplines such as geography, economics, regional science, atmosphere, geophysics, and hydrology provide knowledge and mechanisms.
In addition to the spatial analysis module bundled with GIS software, there are also some dedicated spatial analysis software, such as GISLIB, SIM, PPA, Fragstats, etc.
Data Modeling
Relating wetland maps to rainfall recorded at different places such as airports, TV stations and schools is difficult. However, GIS can describe the two- and three-dimensional characteristics of the surface, underground and atmosphere.
For example, GIS can quickly map rain gauge lines that reflect rainfall.
Such a graph is called a rainfall line graph. The method of estimating the characteristics of the entire surface by measuring a limited number of points is already well established. A two-dimensional rainfall line chart can be overlaid and analyzed with other layers in the same area in GIS.
Topological Modeling
Have any gas stations or factories operated near the wetland in the past 35 years? Are there any such facilities that meet the criteria of being within 2 miles and above the wetlands? GIS can identify and analyze this spatial relationship in digital spatial data. These topological relationships allow complex spatial modeling and analysis. The topological relationships of geographic entities include connection (what is connected to what), inclusion (what is within what), and proximity (the distance between the two).
Network Modeling
If all factories near wetlands 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 an environmentally damaging amount? GIS can simulate the diffusion path of pollutants along a linear network (river). Values ??such as slope, speed limits, and pipe diameters can be incorporated into the model to make the simulation more accurate. Network modeling is commonly used for transportation planning, hydrological modeling, and underground pipe network modeling.