The core issues of geographic information system can be summarized into five aspects: location, conditions, trends, patterns and models.
1) Locations (Locations)
That’s what’s in a particular place.
First, you must define the specific location of an object or region information, commonly used definition methods are: determine the location through various interactive means, or directly input a coordinate; second, after specifying the location of the target or region, you can get the expected results and all or part of their characteristics, such as the current plot owner, address, land use, valuation, and so on.
That is, where there is something that meets certain conditions.
First, you can specify a set of conditions, such as selecting from predefined options; filling in logical expressions; and interactively filling in forms on terminals.
Secondly, after specifying the conditions, you can get a list of all the objects that meet the specified conditions, such as showing all the features that meet the specified conditions on the screen with high brightness, such as the land type in which it is located, the valuation is less than $200,000, four bedrooms and a wooden house.
Such problems need to integrate existing data in order to identify geographical phenomena that have occurred or are changing.
First of all, to determine trends, of course, the determination of trends does not guarantee that each time is correct, once a specific data set is mastered, the determination of trends may depend on hypothetical conditions, personal speculation, observation phenomena or evidence reports.
Secondly, in view of this trend, we can confirm or negate it by analyzing the data. Geographic information systems allow users to quickly obtain quantitative data and charts illustrating the trend. For example, through GIS, the characteristics of this trend can be identified: how many citrus plots have been converted to other uses? What’s the use now? How many such changes have taken place in a region? How many years can this change be traced back? Which time period best reflects this trend? One year, five years or ten years? Has the rate of change increased or decreased?
Such problems are related to the analysis of events that have occurred or are occurring. Geographic Information System (GIS) combines existing data to better explain what is happening and find out which data is relevant to what happened.
Firstly, the determination of patterns usually requires long-term observation, familiarity with existing data and understanding of the potential relationship between data.
Secondly, after the mode is determined, a report can be obtained showing when and where the event occurred and a series of maps showing the event. For example, motor vehicle accidents often conform to a specific pattern, where does the pattern (accident) occur? Does the place of occurrence have anything to do with the time? Is it at a particular intersection? What are the conditions at these intersections?
The solution of this kind of problem needs to establish a new data relationship to produce a solution.
Firstly, models are established, such as selection criteria, testing methods, etc.
Secondly, after establishing one or more models,which can generate a list that satisfies all the specific features, emphasizing the map of the selected features, and providing a detailed description of the selected features. For example, to build a children’s bookstore, the evaluation indicators for site selection may include 10, 15, 20 minutes of reachable space. The number of children aged 10 or under living nearby, the income of nearby families and potential competition around them.
In order to accomplish the core tasks of the above GIS, different functions are needed to implement them. Although the advantages and disadvantages of commercial GIS software packages are different, and the technologies they use to implement these functions are different, most commercial GIS software packages provide the following functions: Data Acquisition, Preliminary data Processing, Storage and Retrieval, Search and Analysis, Display and Interaction .
Figure 1-8 illustrates the relationship between these functions and the different representations of their Manipulation data.
As can be seen from Figure 1-8, data acquisition is the acquisition of data from observations in the real world, as well as from existing documents and maps. Some data are already in digital form, but data preprocessing is often needed to convert the original data into structured data so that it can be queried and analyzed by the system. Query analysis is to obtain a subset of data or transform it, and interact with the actual results. In the whole process of processing, data storage and retrieval as well as interactive performance support are needed. In other words, these two functions run through the whole process of GIS data processing.
** Six components of spatial information processing and analysis [Ding Yuemin]**
Spatial operations, such as map union, intersection, subtraction, buffer calculation, selection, etc.
Spatial statistical analysis is used to describe and analyze the relationship between spatial data, such as spatial autocorrelation analysis.
Spatial model, focusing on spatial phenomena, spatial structure, spatial relations and spatial location analysis, such as network analysis and water system generation, etc.
Spatial representation/visualization, focusing on the expression of spatial information;
Spatial database management, including spatial database design, spatial data structure, spatial data management and spatial query.
Spatial model base management, including model management for spatial decision support system, etc.
It is mainly used to obtain data, to ensure the integrity of data in the GIS database in terms of content and space, numerical logic consistency and correctness. In general, the construction of a GIS database accounts for 70% or more of the total system construction investment, and this ratio will not change significantly in the near future. Therefore, information sharing and automated data input have become an important part of GIS research; at present, there are many methods and technologies that can be used for GIS data collection, and some are only used for geographic information systems, such as hand-held tracking digitizers;
The data processing of the steps mainly includes data formatting, conversion, and generalization. The formatting of data refers to the transformation between data of different data structures, which is a time-consuming, error-prone, and requires a large amount of computation, and should be avoided as much as possible; data conversion includes data format conversion, data scale change, etc. In the way of data format conversion, vector to raster conversion is faster and simpler than its inverse operation. The transformation of the data scale involves the scaling of the data scale, translation, rotation, etc., the most important of which is the projection transformation; generalization includes data smoothing, feature aggregation, etc. At present, the data summary function provided by GIS is extremely weak, and there is still a big gap between the requirements of map synthesis and further development.
This is a key step in the establishment of a GIS database, involving the organization of spatial data and attribute data. Raster models, vector models, or raster/vector hybrid models are commonly used methods of spatial data organization. The choice of spatial data structure determines the function of data and analysis that the system can perform to a certain extent; in the organization and management of geographic data, the most important thing is how to integrate spatial data with attribute data. At present, most systems store the two separately and connect them through common items (generally defined as feature identifiers). The disadvantage of this organization is that the definition of data is separated from the data operation, and it is impossible to effectively record the changing properties of the feature in the time domain.
Spatial query is the most basic analytical function that GIS and many other automated geographic data processing systems should have; spatial analysis is the core function of geographic information system, and it is also the fundamental difference between geographic information system and other computer systems, model analysis is to analyze and solve the space-related problems in the real world with the support of geographic information system, which is an important indicator of the deepening of GIS applications. The spatial analysis of geographic information systems can be divided into three different levels.
It includes retrieving spatial objects and their attributes from spatial locations and retrieving spatial objects from attribute condition sets. Spatial index is the key technology of spatial retrieval. How to retrieve the required information from large-scale GIS database effectively will affect the analysis ability of GIS; on the other hand, the graphical expression of spatial objects is also an important part of spatial retrieval.
Spatial topology overlay realizes the union of input element attributes and the spatial connection of element attributes. The essence of spatial topological superposition is Boolean operation in spatial sense.
In terms of spatial model analysis, most of the current research work focuses on how to combine GIS with spatial model analysis. Its research can be divided into three categories:
The first is the spatial model analysis of the external geographic information system, which regards the geographic information system as a general spatial database, while the spatial model analysis function relies on other software.
The second is the analysis of spatial models within GIS, which attempts to use GIS software to provide spatial analysis modules and develop a macro language for problem solving models, this method is generally based on the complexity and diversity of spatial analysis and is easy to understand and apply, however, the spatial analysis functions provided by GIS software are very limited, this tightly coupled spatial model analysis method is less used in the design of actual geographic information systems;
The third type is the hybrid spatial model analysis, which aims to make the best use of the functions provided by GIS and give full play to the initiative of users of GIS.
Geographic Information System (GIS) provides users with many tools for the representation of geographic data in the form of either computer screen display or hard copy maps such as reports, tables and maps, especially the map output function of GIS. A good geographic information system should provide a good, interactive mapping environment for users of GIS to design and produce high quality maps.