Geographic Information System Knowledge Points

What is GIS Part 1: Basic Concepts of GIS

(a) Data and Information

Data is an unprocessed source material that can be digitized or recorded to be be identified by the symbols. Numbers, words, symbols, and images are all data.

Information (Information) is the use of words, numbers, symbols, language, images and other media to represent the content, quantity or characteristics of events, things, phenomena, etc., so as to provide people (or the system) with new facts and knowledge about the real world, as the basis for production, construction, management, management, analysis and decision-making. Information is characterized by objectivity, applicability, transmittability and *** enjoyment. Information comes from data (Data).

Data is a representation of the objective object, and information is the meaning of the data connotation, the content and interpretation of the data. For example, from the field or social survey data can be obtained from a variety of specialized information; from the measurement data can be extracted from the ground target or object shape, size and location and other information; from the remote sensing image data can be extracted from a variety of features of the graphic size and thematic information.

(ii) geographic information

Geographic information is the sum of numbers, words, images and graphics that characterize the quantity, quality, distribution characteristics, connections and patterns of the elements or substances inherent in the geosphere or geographic environment. Geographic information is the characterization and all useful knowledge about the nature, features and state of motion of geographic entities, and it is the interpretation of geographic data that expresses the relationship between geographic features and geographic phenomena. Geographic data, on the other hand, is a symbolic representation of the relationship between various geographic features and phenomena, including three parts: spatial location, attribute features (referred to as attributes) and temporal features. Spatial location data describes the location of a feature. This location can be defined according to the geodetic reference system, such as the geodetic latitude and longitude coordinates, and can also be defined as the relative positional relationship between features, such as spatial adjacency, containment, etc. Attribute data, sometimes also known as non-spatial data, is a qualitative or quantitative index belonging to a certain feature and describing its characteristics. Time domain features are the moments/times when geographic data are collected or geographic phenomena occur. Temporal data are very important for environmental simulation and analysis and are receiving more and more attention from the GIS community. Spatial location, attributes and time are the three basic elements of geospatial analysis.

Geographic information in addition to the general characteristics of information, but also has the following unique characteristics:

(1) spatial distribution. Geographic information has the characteristics of spatial positioning, first positioning and then qualitative, and in the region to show the distributed characteristics of its attributes manifested in multiple levels, so the distribution or update of the geographic database should also be distributed.

(2) large amount of data. Geographic information has both spatial characteristics, and attribute characteristics, in addition to geographic information also changes with time, with time characteristics, so its data volume is very large. Especially with the continuous development of the global earth observation program, we can get every day on the earth's resources, environmental characteristics of the trillion trillion trillion of data. This inevitably puts a lot of pressure on data processing and analysis.

(3) the diversity of information carriers. The first carrier of geographic information is the material and energy of the geographic entity itself, in addition to describing the geographic entity of the text, numbers, maps and images and other symbolic information carriers, as well as paper, tapes, CD-ROMs and other physical media carriers. For maps, it is not only the carrier of information, but also the medium of information dissemination.

(C) Geographic Information System

Geographic Information System (GeographicInformationSystem or Geo-Informationsystem, GIS) is sometimes called "Geographic information system" or "resource and environmental information system". It is a specific and very important spatial information system. It is a technical system that collects, stores, manages, calculates, analyzes, displays and describes the relevant geographic distribution data in the space of the whole or part of the Earth's surface layer (including the atmosphere) with the support of computer hardware and software systems. The object of GIS processing and management is a variety of geospatial entity data and its relationship, including spatial positioning data, graphic data, remote sensing image data, attribute data, etc., used to analyze and deal with a variety of phenomena and processes distributed in a certain geographic area, to solve the complexity of the planning, decision-making and management issues.

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

1, the physical shell of the GIS is a computerized technical system, which in turn consists of a number of interrelated subsystems, such as data acquisition subsystems, data management subsystems, data processing and analysis subsystems, image processing subsystems, Data product output subsystems, etc., these subsystems are superior, the structure directly affects the GIS hardware platform, functionality, efficiency, data processing

The way and the type of product output.

2, GIS operation object is spatial data, that is, points, lines, surfaces, bodies, such as three-dimensional elements of the geographic entity. The most fundamental feature of spatial data is that each data are coded according to uniform geographic coordinates, to achieve its positioning, qualitative and quantitative description, which is the fundamental mark of GIS is different from other types of information systems, but also where the technical difficulties lie.

3, GIS's technical advantage lies in its data synthesis, simulation and analysis and evaluation capabilities, can be obtained by conventional methods or ordinary information systems are difficult to obtain important information to achieve the evolution of geospatial processes simulation and prediction.

4, GIS and mapping and geography have a close relationship. Geodesy, engineering surveys, mining surveys, cadastral surveys, aerial photogrammetry and remote sensing technology for GIS in the spatial entity to provide a variety of different scales and accuracy of the positioning of the number; electronic tachymeter, GPS global positioning technology, analytical or digital photogrammetric workstations, remote sensing image processing system and other modern mapping technology, can be direct, rapid and automatic access to the spatial target of the digital information products, to provide GIS with a rich and more real-time information. It provides rich and more real-time information sources for GIS, and prompts GIS to develop to a higher level. Geography is the theoretical basis of GIS. Some scholars assert that "GIS and information geography are the main tools and instruments of the second revolution of geographic science. If the rise and development of GIS is a key to the information revolution of geoscience, then the rise and development of information geography will be a door to open the information revolution of geoscience, and will certainly open up a brand new world for the development and improvement of geoscience".GIS is regarded as the third-generation language of geoscience -

GIS can be divided into global, regional and local according to the size of the scope of the study; according to the different contents of the study can be divided into comprehensive and thematic. Various specialized application systems at the same level can be centralized to constitute a regional integrated system at the same level of the corresponding geographical area. In the planning and establishment of the application system should be unified planning for the development of these two systems to reduce the duplication of very cost, improve the degree of data **** enjoyment and practicality.

What is a geographic information system Part II: Geographic Information System Terminology (collated version)

GeographicInformationSystemGIS as a kind of information technology, is in the computer hard, software support, to geospatial database (GeospatialDatabase). GeospatialDatabase) as the basis, with the spatial connotation of geographic data as the processing object, the use of systems engineering and information science theory, collection, storage, display, processing, analysis, output geographic information computer system for planning, management and decision-making to provide information sources and technical support. Simply put, GIS is to study how to use computer technology to manage and apply the spatial information of the earth's surface, it is an organism composed of computer hardware, software, geographic data and personnel, using geographic modeling and analysis methods, to provide a variety of spatial and dynamic geographic information at the right time for geographic research and geographic decision-making services of the computer technology system. Geographic information systems are spatial information systems.

Geographic information refers to the digital, textual, pictorial, and graphical representations of the quantity, quality, distributional characteristics, connections, and patterns of the elements inherent in the geographic circle or geographic environment; it is spatial information with spatial orientation, multidimensional structural characteristics, and dynamic change characteristics.

Geographic information science and geographic information systems, it is more focused on geographic information as a science, rather than just a technical realization, the main research in the application of computer technology to geographic information processing, storage, extraction, and management and analysis of a series of basic issues raised in the process. Geographic information science for geographic information technology research at the same time, but also pointed out the importance of supporting the development of geographic information technology basic theory research.

Geographic data is the data that describes the natural, social and human landscape with reference to the spatial location of the earth's surface, mainly including numbers, text, graphics, images and tables.

Geographic information flow, that is, geographic information from the real world to the conceptual world, then to the digital world (GIS), and finally to the application domain.

Data are symbols that can be identified by digitizing or recording them, representations of objective objects, expressions of information, and become information only when they have an impact on the behavior of the entity.

An information system is a system with the ability to capture, manage, analyze, and express data in a way that provides useful information for a single or organized decision-making process. It includes four major elements: computer hardware, software, data, and users.

The quadtree data structure is a recursive partitioning of a spatial region according to four quadrants (2n × 2n with n ≥ 1) until the values in the subquadrants are monotonic. Any cell whose value (feature code or type value) is monotonic is used as the last storage unit, regardless of the size of the cell. In this way, for the same spatial element, the size of its regional grid varies with the distribution characteristics of the element.

Irregular triangular mesh model referred to as TIN, which is based on the region of a finite set of points to divide the region into a network of connected triangular surfaces, any point in the region falls on the vertices, edges or triangles of the triangular surfaces. If the point is not on a vertex, the elevation value of the point is usually obtained by linear interpolation (using the elevations of the two vertices of the edge for edges, and the elevations of the three vertices for triangles).

Topological Relationships Topological relationships are the spatial relationships between the nodes, arc segments, and surface domains of the elements of a net structure, which are mainly manifested as topological adjacencies, topological associations, and topological containment. According to the topological relationship, without using coordinates or distance, it can determine the positional relationship of one geographic entity relative to another, and the topological data is also conducive to the query of spatial elements.

Topological structure for the establishment of associations between points, lines and polygons, as well as a thorough solution to the problem of neighboring and islanding information processing and must establish a data structure. Such a structure should include the following: unique identifiers, polygon identifiers, pointers to outsourced polygons, pointers to neighboring polygons, boundary links, ranges (maximum and minimum x and y coordinate values).

Swim coding is to merge neighboring grids with the same value row by row, and record the value of the merged grid and the length of the merged grid, which is aimed at compressing the amount of raster data and eliminating redundancy between data.

Spatial data structure refers to the logical structure of geographic graphics suitable for storage, management, and processing by computer systems, and is an abstract description of the spatial arrangement and interrelationships of geographic entities.

Vector data structure is a data organization that uses points, lines, surfaces, and their combinations in Euclidean geometry to represent the spatial distribution of geographic entities. This data organization can best approximate the spatial distribution characteristics of geographic entities, with high data accuracy and low redundancy of data storage, which is convenient for network analysis of geographic entities, but it is difficult to analyze the superposition of multi-layer spatial data.

Grid data structure based on the raster model of the data structure referred to as the raster data structure, refers to the space partitioned into a regular grid, in each grid to give the corresponding attribute values to represent the geographical entity of a form of data organization.

Spatial index refers to a data structure that is arranged in a certain order based on the location and shape of spatial objects or some kind of spatial relationship between spatial objects, which contains summary information of spatial objects. As an auxiliary spatial data structure, the spatial index is between the spatial operation algorithm and the spatial objects, and it is filtered by a large number of spatial objects unrelated to a specific spatial operation are excluded, so as to improve the speed and efficiency of spatial operations.

Spatial data coding is the process of representing the results of data classification in a symbolic system that is easily recognized by computers and people. The purpose of coding is to provide geographic categorization and characterization of spatial data, as well as to facilitate the input, storage, and management of geographic elements, and the need for data exchange and **** sharing between systems.

The Delaunay triangulation, which is a triangulation of Deloni triangles, is the triangulation that performs best in terrain fitting and is therefore often used for TIN generation. Delaunay triangles are formed by connecting the three closest neighboring points, and the Voronoi polygon corresponding to these three neighboring points has a common*** vertex, which is also the center of the outer circle of the Delaunay triangle.

Voronoi polygons, or Tyson polygons, use an extreme method of boundary interpolation, using only the nearest single point to interpolate the region. The Tyson polygon splits the region into sub-regions by data point location, each containing one data point, with the distance of each sub-region to the data points within it being less than any distance to any other data point, and assigning values using the data points within it.

The raster data compression codes are key codes, tour length codes, block codes, and quad-tree codes. Its purpose, is to record as much information as possible with as little data as possible, and its type and information lossless coding and information lossy coding points.

Boundary Algebraic Algorithm Boundary Algebraic Polygon Filling Algorithm is a vector format to raster format conversion algorithm based on the idea of integrals, which is suitable for the record of topological relations of polygonal vector data converted to raster structure. Instead of judging the relationship with the boundary point by point to complete the conversion, it dynamically assigns the boundary position information to each raster point according to the topological information of the boundary through simple addition and subtraction algebraic operations, realizing the high-speed conversion from vector format to raster format without considering the relationship between the boundary and the search trajectory, so the algorithm is simple and reliable, and each boundary arc segment is searched only once, avoiding the repeated calculation.

DIME file The U.S. Census Bureau proposed the Double Independent Map Encoding File (DIME) for the 1980 census. It contains geostatistical data codes obtained from surveys and coordinate values for the boundaries of metropolitan areas, and provides outline maps of city streets, address ranges, and geostatistical codes associated with the Census Bureau's tabulation statistics. TIGER replaced the DIME file in the 1990 Census.

Spatial data interpolation is the method of extrapolating data from a known point or partition to an arbitrary point or partition. Spatial data compression is the extraction of a subset A from the obtained data set S. This itself serves as a new source of information that best approximates the original set within the specified accuracy range, while achieving the largest possible compression ratio.

Coordinate transformation is essentially the establishment of a one-to-one correspondence between two planar points, including geometric corrections and projection transformations, and they are one of the basic elements of spatial data processing.

The affine transformation is one of the most used geometric correction methods in GIS data processing. Its main characteristics are: at the same time take into account the deformation of the actual scale in the x and y directions caused by the geodesic deformation, so the corrected coordinate data in different directions will change the length ratio.

Data precision is an aspect of data quality that examines how well the phenomenon is described in detail. Data with low precision is not necessarily less accurate.

A spatial data engine is an implementation of a spatial database management system that adds a layer of spatial database engine on top of a conventional database management system to gain the ability to store and manage spatial data beyond the functionality of a conventional database management system. A representative is ESRI's SDE.

Spatial data engine provides an open interface between users and heterogeneous spatial database data, and it is a middleware technology between application programs and database management systems. Customers using GIS from different vendors can submit their own data to a large relational DBMS through the spatial data engine, which is managed centrally by the DBMS; similarly, customers can obtain data from other types of GIS from a relational DBMS through the spatial data engine and transform it into a way that customers can use.

A database management system is a software system that operates and manages databases, provides software systems that can be called by multiple applications and users, and supports the creation, updating, querying, and maintenance functions of databases that can be called by multiple applications and users.

The spatial database is the sum of geospatial data related to the application stored on the physical computer storage medium of the geographic information system, generally in the form of a series of specific structural files organized on top of the storage medium.

A spatial data model is a conception of real-world spatial entities and their interconnections that provides a basic methodology for describing spatial data organization and designing spatial database schemas. In general, the GIS spatial data model consists of a conceptual data model, a logical data model, and a physical data model in three organically linked levels.

Distributed database is a collection of data that is physically distributed in different nodes of the computer network, while logically belonging to the same system. It is distributed and at the same time logically interconnected.

Object-relational management model / type refers to the expansion of relational databases, through the definition of a series of operations on spatial objects (such as points, lines, surfaces) API functions, to directly store and manage unstructured spatial data spatial database management model.

Buffer analysis is based on the analysis of the object of the point, line, surface entities, automatically establish them around a certain distance from the band zone, to identify these entities or subjects on the neighboring objects of the radiation range or degree of influence, in order to provide a basis for a certain analysis or decision-making.

Stacking analysis refers to stacking the layers of two geographic objects in the same area each time under the conditions of a unified spatial reference system to produce multiple attribute characteristics of the spatial region or to establish spatial correspondences between geographic objects.

Spatial analysis is an analysis technique based on spatial data, which is based on the principles of geography, and through analysis algorithms, obtains information about the spatial location, spatial distribution, spatial morphology, spatial formation, and spatial evolution of geographic objects from spatial data.

Network analysis is a basic model in the operations research model, that is, geographic analysis and modeling of geographic networks and urban infrastructure networks. Its fundamental purpose is to study and plan how a network project can be arranged and run in the best possible way.

Perspective drawing from the digital elevation model is an extremely important application of DEM. Perspective three-dimensional map can better reflect the three-dimensional shape of the terrain, very intuitive. Compared with the use of contour lines to indicate the shape of the terrain

has its own unique advantages, closer to people's intuitive vision. Adjusting the point of view, the angle of view and other parameters, you can draw from different directions, different distances, different forms of perspective animation.

The network is a binary system of points and lines, usually used to describe the movement of a resource or material in space.

Variable screening analysis is a spatial statistical analysis method that simplifies interrelated complex multivariate data by finding a set of mutually independent variables. Commonly used are principal component analysis, principal factor analysis, key variable analysis and so on.

Variable cluster analysis is a set of data points or variables, according to their degree of proximity in the nature of the classification of spatial statistical analysis methods. The similarity of two data points in m-as-space can be measured by the distance of these points in variable space.

A digital terrain model, or DTM, is a vector sequence of finite terms defined over a two-dimensional region that simulates a continuous distribution of terrain in terms of a discrete distribution of planar points.

Digital Elevation Model When the ground attribute of a digital ground model is elevation, the model is a digital elevation model.

GIS application model is based on specific application goals and problems, with the help of GIS's own technical advantages, so that the conceptual model formed in the conceptual world, materialized into the information world can be operated in the mechanism and process.

OGC is the OpenGIS Consortium (OpenGISConsortium), whose purpose is to enable users to openly manipulate heterogeneous geographic data, and to promote the use of new technologies and business methods to improve the interoperability of geographic information processing (Interoperablity), OGC members mainly include GIS-related computer hardware and software manufacturers, data producers, and some higher education institutions. OGC members include GIS-related computer hardware and software manufacturers, data producers, and some universities, government departments, etc. Its technical committee is responsible for the development of specific standards.

OpenGIS (OpenGeodataInteroperationSpecification, OGIS-open geographic data interoperation specification) proposed by the U.S. OGC (Open Geographic Information System Association). Its goal is to develop a specification that allows application developers to use any geodata and geoprocessing distributed over the Web in a single environment and a single workflow. It is committed to eliminating the barriers between geographic information applications as well as between geographic applications and other information technology applications, and to establish a "borderless", distributed, component-based geographic data interoperability environment. Compared with traditional geographic information processing technologies, GIS software based on this specification will have good scalability, upgradability, portability, openness, and flexibility.

A data structure is an abstract description of the data organization of geographic entities and their interrelationships.

Spatial data quality is a measure of the accuracy, consistency, completeness, and unity between spatial data in expressing spatial location, spatial relationships, thematic features, and time, generally described as the reliability and precision of spatial data and expressed in terms of error.

Digital Earth is to digitize and network the vast and complex Earth data into an Earth information model plan. It is an expression of the Earth that can be embedded in massive geographic data, multiple resolutions, and three dimensions, and is a digital reproduction and understanding of the unity of the real Earth and its related phenomena. Its core idea is twofold: first, to use digital means to deal with Earth issues in a unified way; second, to maximize the use of information resources.

Virtual reality, also known as the virtual environment or artificial reality, is a computer-generated advanced human-computer interaction system, that is, constituting a visual experience-based, but also includes auditory, tactile, olfactory perceptible environment, the rehearsal of the special equipment can be realized in this environment to observe, touch, operate, test and other experiments, there is a sense of immersion.

Map projection is to establish a point on the plane (expressed in plane rectangular coordinates or polar coordinates) and the point on the surface of the earth (expressed in latitude and precision) between the function relationship.

A projection transformation is a change from one map projection to another. In essence, it establishes a one-to-one correspondence between the two planar fields and the bi-directional continuum of points in the neighborhood.

The virtual geographic environment, abbreviated as VGE, is a virtual reality based on geographic analysis models, geographic engineering, etc. It is a virtual information geographic world that expresses and describes the spatial distribution of geographic systems and process phenomena established by geoscientists based on observational experiments, theoretical assumptions, etc. It is a virtual laboratory on geographic systems that allows geoscientists to design and modify geographic spatial relationship models in accordance with their personal knowledge, assumptions, and willingness to design and modify geographic spatial relationship models. It allows geoscientists to design and modify geospatial relationship models, geoanalytical models, and geoengineering models according to their personal knowledge, assumptions, and wishes, and to directly observe the results of the interactions, and to obtain the laws of geoscience through multiple cycles of feedback.

Gauss-KruegerProjection① is a transverse-axis equal-angle tangent elliptic column projection. It is an ellipsoidal column cut across the ellipsoid of the Earth, the ellipsoidal surface and the ellipsoidal surface of the tangent line for a meridian, the projection will be referred to as the central meridian, and then according to certain constraints that is the projection conditions, the central meridian of the central meridian of the two sides of the specified range of points projected onto the ellipsoidal surface to get the Gaussian projection of the point.

② an equirectangular transverse elliptic column projection. The projection strip is projected as a straight line of constant length from the central meridian, and the equatorial projection is also straight and orthogonal to the central meridian.

UTM projection global transverse Mercator projection. It is a variant of the transverse Mercator projection used by the United States to prepare military maps and Earth resource satellite images of the world. It stipulates that the central meridian length ratio is 0.9996.

Electronic map when the paper map through the computer graphic image system optical - electrical conversion quantified as a dot matrix digital image, by image processing and curve vectorization, or direct handheld tracking digitized to generate can be for the geographic information system to display, modify, label, roaming, calculation, management and management of the geographic information system, the map can be used for the geographic information system to display, modify, label, roaming, calculation, management and management of the geographic information system.

Metadata [spatial] refers to the data describing spatial data, which describes the content, quality, representation, spatial reference, management, and other characteristics of the spatial dataset, and is the basis of spatial data exchange, and is also the guarantee of spatial data standardization and norming, which, to a certain extent, provides a guarantee for the quality of spatial data.

Web Geographic Information System (WebGIS) is a combination of Web technology and GIS technology, that is, the use of Web technology to extend and improve the geographic information system of a new technology. From any node of the WWW, Internet users can browse the spatial data in the WebGIS site, produce thematic maps, and conduct a variety of spatial search and spatial analysis.

GIS interoperability Interoperability refers to two or more entities in a heterogeneous environment that can communicate and collaborate with each other to accomplish a particular task, despite the different languages, execution environments, and models on which they are based. These entities include applications, objects, system runtime environments, etc. Spatial data interoperability for heterogeneous databases and platforms, to achieve interoperability of data processing, compared with data conversion, it is a "dynamic" data *** enjoyment, independent of the platform, with a high degree of abstraction, is the direction of development of spatial data *** enjoyment.

Component GIS is a GIS system (including the basic platform and application system) that uses object-oriented technology and component software. The basic idea is to divide the major functional modules of GIS into several components, each of which accomplishes different functions. Between each GIS component, as well as between GIS components and other non-GIS components, can be easily integrated through visual software development tools to form the final GIS base platform and application system.

The client/server architecture, or C/S architecture, is a distributed system architecture in which the client is usually the application system that interacts with the end user, and the server consists of a set of collaborative processes that provide services to the client. Clients and servers usually run the same microkernel, and a client/server mechanism can have multiple clients, or multiple servers, or both. The client/server model is based on a simple request/response protocol, in which the client makes a request to the server for information processing, the server receives the request and decodes it, performs the appropriate operation based on the contents of the request, and transmits the results of the operation