First of all, in order to better understand what GIS is, what it is and what it can do, we must first understand some basic concepts of GIS.
First of all, I will introduce seven aspects related to it, namely, information and data, geographic information, geographic information system, its composition, its characteristics, and then its functions and related disciplines of geographic information system.
1. 1 information and data
Information: Information provides people or machines with all kinds of knowledge about the real world through numbers, characters, symbols, languages, graphics, images and sounds. Information has the characteristics of objectivity, applicability, transferability and enjoyment. Information comes from data.
Data refers to all objects that can be processed by computers, including numbers, characters, symbols, graphics, images and so on. It is a raw material, and its format depends on the computer system.
Data is the representation of objective objects, and information is the meaning of data connotation, which is the content and interpretation of data. Information and data are inseparable. In other words, data is the carrier of information. Only by understanding the meaning of data can we get the information contained in the data.
Information can exist independently from the information system, or it can exist independently from all components and stages of the information system; The format of data is usually related to the computer system and varies with the form of the physical device that loads it. Data is the original fact, and information is the result of data processing. People with different knowledge and experience will get different information when they understand the same data.
Information and data refer to generally speaking, we mainly refer to geographic information and geographic data in geographic information system. The so-called geographic information refers to the general name of numbers, characters, images and graphs that represent the quantity, quality, distribution characteristics, mutual relations and changing laws of various elements of a geographic system. Refers to the sum of information directly or indirectly related to geographical spatial location distribution and time development. Geographic information belongs to spatial information, which is the interpretation of geographic data expressing the relationship between geographical features and geographical phenomena. Its location identification is linked with data, which is the most remarkable sign that geographic information is different from other types of information. Geographical data is a symbolic representation of the relationship between various geographical features and phenomena, including three parts: spatial position, attribute characteristics and time domain characteristics.
Spatial position is the position of ground objects that we can see through the latitude and longitude network or the kilometer network.
Attribute data is a qualitative or quantitative index to describe the characteristics of ground objects;
Time domain characteristics refer to the time or period when geographic data collection or geographic phenomena occur. Spatial position, attribute and time are three basic elements of geospatial analysis.
Geographic information system is called GIS for short. Different application fields and different majors have different understanding and interpretation of GIS. It is impossible to explain the concept of GIS in a few simple sentences. At present, there are many definitions of geographic information system at home and abroad. Generally, GIS is defined as follows:
Geographic information system is a computer system for collecting, storing, managing, processing, retrieving, analyzing and expressing geospatial data.
B. Geographic information system consists of computer system, geographic data and users. Through the integration, storage, retrieval, operation and analysis of geographic data, various geographic information is generated and output.
Wait a minute.
Some of these definitions focus on the technical connotation of GIS, while others emphasize the application function of GIS. The more widely known definition of GIS is that of the United States Federal Digital Map Coordination Committee. This definition holds that "GIS is a system composed of computer hardware, software and different methods. The system design supports the collection, management, processing, analysis, modeling and display of spatial data, thus solving complex planning and management problems. "
So we can see the conceptual framework and composition of GIS. The top layer is user interface, the middle layer is system and database management, and the bottom layer is database establishment, spatial data processing and product generation and output.
A practical GIS should support the collection, management, processing, analysis, modeling and display of spatial data, and its basic components generally include the following five main parts: system hardware, system software, spatial data, application personnel and application model.
System hardware mainly refers to GIS host, GIS external equipment and GIS network equipment.
System software mainly refers to GIS professional software, database software and system management software.
GIS professional software generally refers to general GIS software with rich functions, including various advanced functions for processing geographic information, which can be used as a platform for other application systems. Its representative products are ARC/INFO, Gio Star, MapInfo, MapGIS, GeoStar and so on. Details will be introduced later.
1. Spatial coordinate data
The operating object of geographic information system is spatial data, which specifically describes the spatial characteristics, attribute characteristics and time characteristics of geographic entities.
There are many data sources and types of GIS, which can be summarized as follows: map data comes from various types of ordinary maps and thematic maps; Image data mainly comes from satellite remote sensing and aerial remote sensing, including multi-platform, multi-level, multi-sensor, multi-temporal, multi-spectral and multi-resolution remote sensing image data; Terrain data comes from the digitalization of topographic contour map. And other types of data.
2. Application personnel
GIS application personnel include system developers and end users of GIS technology.
3. Application model
Such as land suitability model, park location model, flood forecasting model, soil erosion model, forest growth model and so on. The characteristics of geographic information system include three aspects, one is spatial visualization, the other is spatial orientation, and the third is spatial thinking.
For example, with a chinese administrative division map, we can extract the population data of 1994 from the database of GIS, calculate the population density, and display the patches corresponding to administrative divisions with different colors and filling methods according to the grading index of population density, so that the thematic attribute characteristics of spatial features can be visualized with spatial reference information through GIS tools.
Spatial orientation
Using geographic information system, we can not only survey the whole area of the study area, but also use the basic functions provided by GIS, such as zooming and roaming, to go deep into the areas we are more interested in.
Spatial thinking
Such as buffer analysis, overlap analysis, etc. To generate information that is not stored in GIS spatial database.
The spatial thinking function of GIS enables us to reveal tasks that other types of information systems cannot accomplish, such as spatial relations, spatial distribution patterns and spatial development trends.
1.6 brief introduction to the functions of geographic information system
The functions of GIS mainly include two aspects
1. is a basic function, mainly including 1. Data collection in editing II. Data storage in management. Data processing and conversion, including data conversion, data reconstruction, data extraction 1.4 topological superposition, buffer establishment, digital terrain analysis, spatial set analysis and other spatial analysis and statistics 1.5 product production and display 1.
2 Application function
2. 1 resource management
The inventory, management and analysis of resources are the most widely used fields of GIS, and also the main mature application fields in this area at present, including forest and mineral resources management, wildlife protection, land use planning and so on.
2.2 Regional planning
For example, planners use GIS to analyze traffic flow, land use and population data and predict future road grades; Engineers use GIS to combine address, hydrology and human data to design routes and structures.
2.3 Land monitoring
GIS method and multi-temporal remote sensing data can be effectively used for forest fire prediction, flood disaster monitoring and inundation loss estimation, land use dynamic change analysis and environmental quality evaluation. For example, Research on Flood Control and Disaster Reduction in the Yellow River Delta Region shows that with the support of ARC/INFO geographic information system, by establishing a large-scale digital terrain model and obtaining relevant spatial and attribute data, the land use and area of multiple flood discharge areas can be calculated, and the losses of houses and property in different flood discharge areas can be compared, so as to determine the best route for personnel evacuation, property transfer and disaster relief materials supply in flood discharge areas, and ensure the effective handling of emergencies at the fastest speed.
2.4 Auxiliary decision-making
For example, GIS can effectively manage spatial data, conduct spatial visualization analysis, determine the location of commercial centers and analyze potential markets, discover the laws of commercial areas, study the trends of business opportunities in time and space, and constantly create new business opportunities for enterprises.
1.7 related disciplines of geographic information system
Geographic information system (GIS) is a new technology of geographical research that has developed rapidly since 1960s, and it is the product of interdisciplinary. As the product of the combination of traditional science and modern technology, geographic information system provides new methods for various disciplines involved in spatial data analysis, and the development of these disciplines provides some technologies and methods to form geographic information system to varying degrees. In order to master and understand GIS better, it is necessary to know and understand the disciplines related to GIS.
2. Cartographic basis of geographic information system
In this part, we mainly introduce geospatial reference, map scale and map projection. This is our earth, but in fact,
The natural surface of the earth is rugged and very irregular, including mountains, hills and plains, as well as rivers, lakes and oceans.
The earth is not a right sphere, but an ellipsoid with a slightly shorter polar radius, a slightly longer equatorial radius, a slightly convex north pole and a slightly flat south pole, almost pear-shaped. This kind of uneven surface can't be expressed by mathematical formula and can't be operated.
So when surveying and mapping, we must find a regular surface to replace the natural surface of the earth. This is the geoid.
Our hypothesis is that when the ocean is at rest, its free water surface must be orthogonal to the gravity direction (vertical direction) of each point on the surface, and we call this surface the horizon. But there are countless levels, one of which coincides with the static average sea level. It is conceivable that this static average sea level passes through the mainland and islands to form a closed surface, which is the geoid.
Although the shape of the geoid is very complicated, it fluctuates slightly on the whole, and it is an ellipsoid that is very close to rotating around the rotation axis (short axis). Therefore, in surveying and mapping, the earth sphere is replaced by a rotating ellipsoid. This rotating ellipsoid is usually called the earth ellipsoid, or simply ellipsoid.
So the earth model is a three-level approximate model. The natural surface of the earth is extremely irregular and cannot be described by mathematical surfaces. The sphere surrounded by the horizon is irregular, dynamic and not unique. Then there is the sphere surrounded by the geoid, which is irregular but relatively unique. Finally, the earth was replaced by a rotating ellipsoid.
Coordinate system classification can be divided into spherical coordinate system and plane coordinate system. The spherical coordinate system is directly established on the spherical surface, and the position of geographical objects is expressed by latitude and longitude. Plane coordinate system is a coordinate system established on a plane, also known as projection coordinate system.
Geodetic latitude and longitude: indicates the position of the ground point on the reference ellipsoid, geodetic longitude L, geodetic latitude? And the height h of the earth.
Geodetic longitude: refers to the dihedral angle between the geodetic meridian plane and the primitive meridian plane at a point on the reference ellipsoid. The prime meridian (or the first meridian) is the starting point of longitude calculation. The longitude of this line is 0 degrees, the east longitude is 0- 180 degrees, and the west longitude is 0- 180 degrees. East longitude is positive and west longitude is negative.
Geodetic latitude: refers to the angle between the perpendicular (normal) of a point on the reference ellipsoid and the equatorial plane. Latitude is calculated from the equator, where the latitude is 0 degrees. The farther the latitude is from the equator, the greater the latitude, and the latitude of the pole is 90 degrees. The north of the equator is called north latitude and the south is called south latitude. North latitude is positive and south latitude is negative.
Elevation coordinate system
The elevation from the ground point to the geoid is called absolute elevation. As shown in the figure, HAHB is the geoid, and the vertical distances HA and HB from ground points A and B to HAHB are the absolute elevations of points A and B. The elevation from ground points to any leveling surface is called relative elevation. As shown in Figure 2, the vertical distances HA' and HB' from two points A and B to any horizontal plane are the relative heights of two points A and B. ..
Types of maps
1. Classification by map mode
Ordinary map is a map that shows the overall characteristics of physical geography and social economy, and does not emphasize a certain element. Thematic map is a map that focuses on one or more thematic elements and their relationships. Thematic map is
2. Classification by scale
Large (≥ 1:65438+ million) and small (≤ 1:65438+ million ~ 1:65438+ million).
1: 5,000, 1: 1,000, 1: 25,000, 1: 1,000, 1,000, 1,250,000.
3. Classification by region
(1) Planet map, Earth map
(2) World map, continental map, etc.
(3) National map, branch map, etc.
⑷ Local area map: sea area map, area map, etc.
map projection
Firstly, it introduces why projection is needed, the essence of map projection, the deformation of map projection and the method of map projection.
The method of mapping points on the ellipsoid of the earth to the plane is called map projection.
Geographical coordinates are spherical coordinates, so it is not convenient to measure parameters such as distance /sitemap.txt, orientation and area.
The ellipsoid of the earth is an unexpanded surface.
The map is flat, which accords with visual psychology and is convenient for calculating distance, orientation and area and analyzing the essence of map projection in various spaces.
Map projection refers to the establishment of a one-to-one correspondence between points on the earth's surface and points on the projection plane.
Map projection: projection deformation
If the unexpanded ellipsoid of the earth is unfolded into a plane, there can be no fracture, and the figure will be pulled out in some places.
Stretching, some places are compressed, so projection deformation is inevitable.
Length deformation, area deformation, angle deformation
Projection methods can be divided into geometric projection and non-geometric projection, and can be divided into equal area projection, isometric projection and arbitrary projection according to deformation law.
Geometric projection is to project the latitude and longitude net on the ellipsoid onto the geometric surface and expand the geometric surface into a plane. It is divided into azimuth projection, cone projection and cylindrical projection.
Projection classification
Deformation classification:
Isometric projection: the angle is unchanged before and after projection.
Equal area projection: the area is unchanged before and after projection;
Arbitrary projection: Angle, area and length are all deformed.
Projection plane:
Transverse cylindrical projection: the projection plane is a transverse cylinder.
Conical projection: The projection plane is a cone.
Azimuth projection: The projection plane is a plane.
Projection plane position:
Orthographic projection: the central axis of the projection plane coincides with the earth axis.
Oblique axis projection: the central axis of the projection plane is oblique to the earth axis.
Transverse projection: the central axis of the projection plane is perpendicular to the earth axis.
Tangent projection: the projection plane is tangent to the ellipsoid.
Tangent projection: the projection plane is tangent to the ellipsoid.
Map Projection: Map Projection in GIS
GIS displays geographic information in the form of maps. The map is a plane, and the geographical information is on the ellipsoid of the earth, so
Map projection is indispensable in GIS.
When geographic data in GIS database is stored in geographic coordinates, it must pass through spatial data with map as data source.
The projection transformation is converted into geographical coordinates; When outputting or displaying, the spatial data represented by geographical coordinates should be transformed into the plane coordinates of the specified projection through projection transformation.
In GIS, the projection mode can be specified according to the needs of users, but when the displayed map is consistent with the scale of the national basic map series, the projection used by the national basic map series is generally adopted.