1.2. Basic concept of WebGIS#
Geographic information system GIS#
With the development of computer, network and database technology and the deepening of application, the development of geographic information system (GIS) technology presents new characteristics and trends, and WebGIS based on Internet is one of them. In addition to being applied to the traditional government management fields such as land, resources and environment, WebGIS is also promoting the rapid development of industries closely related to people’s life, such as vehicle navigation, mobile location service, intelligent transportation, rescue and disaster relief, urban facility management, modern logistics and big data analysis.
With the rapid development and wide use of the Internet, people’s demand for geographic information systems is also increasing. The Internet has become a new GIS operating platform. trend. WebGIS has also really become a tool for the masses. At present, the application of network technology in GIS mainly has three modes: centralized mode, C/S mode and B/S mode. Among them, WebGIS based on B/S mode is a new mode, which is used to solve the problem of C/S mode. The problems faced by WebGIS and meet the needs of users for information management.
The full name of GIS is Geographic Information System, and the full Chinese name is Geographic Information System. It is a technical system that collects, stores, manages, calculates, analyzes, displays and describes the relevant geographical distribution data in the whole or part of the earth’s surface (including the atmosphere) space with the support of computer hardware and software systems. Since the “father of GIS” Roger Tomlinson coined the acronym GIS (Geographic Information System) in the 1960s, the field has changed dramatically. Today, students encounter many of the same basics in related courses such as Geographic Information Science, Surveying and Mapping, and Spatial Information Systems. The G in GIS has been interpreted as “global” and “geospatial”, rather than the original “geographic”; S is also not the original “system”, but “science”, “services” and “studies”. But looking for one word to describe what all of these things have in common, “geospatial” might be the best option.
The most easy-to-understand explanation is that GIS is the use of surveying and mapping to generate paper maps or aerial photography and satellite photography to generate images, and then store these data in the computer, express them in the form of maps or pictures, and then according to actual production, life and Various needs in scientific research, and then provide specific processed data.
The development of Internet technology#
The World Wide Web has changed every aspect of human society, as well as geographic information systems. The convergence of the World Wide Web and Geographic Information Systems has given rise to the emerging field of World Wide Web Geographic Information Systems (WebGIS). Web GIS has developed rapidly since its appearance in 1993, and its unique use and charm have become one of the main attractions for people to use the Internet.
The enormous impact of the World Wide Web and its extensive connectivity has benefited GIS, moving it out of offices and laboratories, into the computers of thousands of households, into the mobile phones of hundreds of millions of people, and GIS is widely used in government, enterprise, education and scientific research and other fields, and penetrates into every aspect of our daily life.
Everything that happens in the world is associated with a place. Knowing where something is and why it is there is crucial for people to make good decisions. GIS (geographic information system; or geographic information science) is a technology and science that deals with issues related to geographic location and can collect, store, manage, analyze, express and share geographic data to help people make correct decisions.
Geographic information system appeared earlier than the Internet. In 1962, Roger Tomlinson developed the world’s first operable geographic information system for the Department of forestry and agricultural development of the federal government of Canada, called “Canadian geographic information system”, which is used for detailed survey, statistics and planning of land use in Canada.
Roger Tomlinson founded GIS and devoted itself to promoting the development of GIS methodology, so it is called “the father of GIS”.
Although GIS is usually used to compile maps, its functions are far more than that. It has powerful analytical functions and can correlate many seemingly unrelated data based on their common geographic location, carry out comprehensive analysis to unearth relationships, laws and trends that are hidden or not easily displayed in spreadsheets or statistical software packages to support people in making scientific decisions. GIS can abstract the real world into a series of spatial data layers, such as land use, elevation, imagery, neighborhoods, roads, and business customers. GIS can combine these layers in a variety of ways to draw a variety of thematic maps, and GIS can further analyze these layers and extract a lot of useful information to solve problems such as the following:
In the past few decades, the development and application of GIS have benefited a lot in many fields. The emergence of the World wide Web provides a broader stage for GIS. Let GIS go to more industries and into thousands of households.
What is WebGIS?#
Before giving a clear definition of WebGIS, it is necessary to distinguish several related concepts, namely: Network GIS, Internet GIS or Internet GIS and World Wide Web GIS (WebGIS). WebGIS is often referred to as Web Mapping in foreign countries. ). Distinguishing these concepts will help to correctly understand and apply WebGIS.
Among all these concepts, network GIS contains the most extensive content, including C/S or B/S mode, multi-layer, distributed GIS applications based on various distributed computing models, which can be based on J2EE framework. , can also be based on distributed computing frameworks such as COM/DCOM and CORBA.
The networks here include local area networks, wide area networks, the Internet, and various wireless networks. The protocol used in network GIS can be either TCP/IP or other protocols at various layers, such as HTTP, WAP, GPRS and Bluetooth protocols.
Internet GIS or Internet GIS is a subset of network GIS, it is a network GIS based on TCP/IP protocol, so it can be deployed and run on the Internet. These GIS can be either C/S mode or B/S mode. Google Earth software of Google is a client software of the C/S mode network map service provided by Google.
Therefore, WebGIS is a B/S mode distributed computer application system based on HTTP protocol in the Internet or Intranet environment to store, manage, analyze, publish and share geographic information.
WebGIS can be regarded as a subset of network GIS and Internet GIS. At the same time, it is a distributed GIS built on higher-level application protocols. It is a technically more complex network GIS. , due to the needs of tasks such as load balancing, other distributed computing models are usually used.
Beginning in the 1980s, a large number of GIS software appeared basically based on C/S architecture, that is, professional GIS software must be installed on the machine first, and then users can use these GIS software according to their needs. Of course, this desktop-side GIS software has its natural advantages, such as relatively simple development, no need for Internet support, more complex functions, and relatively quick response. But at the same time, its shortcomings cannot be ignored. The first thing that bears the brunt is the inconvenience of promotion. The reason for the inconvenience of promotion lies in the natural disadvantages of the C/S system itself: it is not convenient for updating, it is not convenient for cross-platform, and it is not convenient for users to use it without installing the specified client.
Since the beginning of this century, the Internet has entered a stage of explosive growth, and the laying of the network and the improvement of the speed of the network have greatly increased, which provides a solid environment for the development of WebGIS. As a result, more and more GIS systems based on B/S begin to provide services, and with the emergence and maturity of RIA (rich client) technology and AJAX (dynamic web page) technology, WebGIS can basically show the same effects and functions as C/S.The great development of WebGIS is also the demand of users. The large-scale expansion of service providers such as Google Maps and Baidu Maps is the best proof. What is WebGIS is an application direction that presents the functions that GIS can provide to users with B/S technology, so that users can use these GIS functions only on the browser.
The basic characteristics of WebGIS#
Web GIS can be simply defined as GIS based on Web environment. At present, the Internet/Intranet is rapidly expanding and developing at an alarming rate. Under such a situation, how to introduce GIS into the Internet/Intranet world, so that GIS can make full use of the advantages of the Internet, has become an important subject of GIS development research.
From the perspective of system integration, synthesizing the viewpoints of OpenGIS, ESR, and Intergraph, GIS based on the World Wide Web should have the following characteristics: First, Web GIS is an open system. Focus on data sharing, software reuse, cross-platform operation, and ease of integration.
Simply put, it can share geographic data from multiple sources, multiple scales, and stored in different locations; it can integrate with non-GIS systems (such as Delphi) through technical means such as object management, middleware, and plug-ins; and can use Java, CORBA, DCOM and other technologies work together across platforms and support the use of client/server models.
Open systems benefit GIS users, software developers, and system integrators alike. Second, Web GIS is suitable for running in the World Wide Web environment. Integrating GIS software with Web server, through common browsers, users can manipulate network GIS anywhere and enjoy geospatial information services, thereby expanding GIS into a public service system; at the same time, it expands map publishing channels, reduces data distribution costs, and improves degree of geographic data sharing.
Finally, Web GIS supports data distribution and distributed processing. The GIS server provides GIS services for local and remote users, such as geographic data catalog services, geographic data access services, geographic spatial analysis services, geographic model system services, and geographic spatial visualization services. Through interoperability technology, a GIS processing process can be coordinated and completed by multiple GIS servers, which share the distributed data objects and run cooperatively on multiple different platforms to maximize the use of network resources.
The composition of WebGIS#
To understand the concept of WebGIS, you should pay attention to the following points:
HTTP protocol: Among many web technologies, HTTP is the main protocol used by servers and clients to communicate with each other.
The simplest WebGIS is a two-tier architecture, consisting of a server and one or more clients. WebGIS includes not only the client you see, but also the server that the client depends on, which may be a server on the Internet or a cloud computing center. Sometimes the server and client can be installed on the same computer, but logically they are still two separate units.
A single WebGIS is usually a three-tier architecture, including data layer, logic layer (or middle layer) and client (or presentation layer). With the popularity of the geographic aggregation (mashup; see Chapter 4) approach, a WebGIS often leverages the services of one or more other WebGIS to form an n-tier (n > 3) structure.
WebGIS and desktop GIS are constantly infiltrating each other. On the one hand, WebGIS relies on desktop GIS to create basic resources such as data and maps; on the other hand, desktop GIS is also expanding, gradually incorporating the functions of WebGIS. For example, ArcMap, a traditional desktop GIS, has also joined the functions of WebGIS and can be used as a client of WebGIS. For example, you can use basemaps from ArcGIS Online, the US Geological Survey, Microsoft Bing Maps, or others in ArcMap without having to purchase and install the basemap data yourself. The open source desktop software QGIS also has the function of publishing map services.
Geographic information system is mainly composed of hardware, software, data and users. The distance between these components is increasing and further separated. This phenomenon is very interesting. In the 1960s and 1970s, these components of GIS were usually installed on a computer. In WebGIS, these components are further separated, and the client and server can be separated from each other. With the advent of technologies such as Web services and aggregation (mashups; see Chapter 4), one client can use the data of one server and the analysis functions of another, which further separates the various components of GIS.
The essential key elements of WebGIS are as follows:
The server has a URL so that the client can find it on the Web;
The client sends the request to the server according to the HTTP specification;
The server performs the requested GIS operation and sends a response to the client via HTTP;
The geographic information system establishes a mathematical model for the surface information, and uses computer technology to store, process and analyze the data. Among them, the geographic information system that uses Web technology is WebGIS. The key features of WebGIS are object-oriented, distributed and interoperable. It encapsulates GIS data and functions into objects, and these objects support distributed computing and can be stored on different servers; objects can be exchanged and interacted easily through a consistent communication protocol.
WebGIS is World Wide Web GIS, which is a B/S mode InternetGIS. From a technical point of view, WebGIS should have the following basic characteristics:
Publish dynamic web applications through a web server.
The client is a common web browser, such as IE, Firefox, etc.
The user interacts with the map through a web browser.
WebGIS is a distributed GIS in B/S mode based on HTTP protocol.
It uses HTTP protocol to realize the communication between the browser and the web server. Users send requests to the web server through the web browser. The server usually returns interactive documents, document fragments or geographic data in other formats in HTML or XML format containing map information to users.
Advantages of WebGIS#
Compared to traditional desktop or LAN-based GIS, Web GIS has the following advantages:
Customers can access the latest data on multiple servers located in different places at the same time, and this unique advantage of Internet/Intranet greatly facilitates the data management of GIS, and makes the data management and synthesis of distributed multiple data sources easier to achieve.
No matter what kind of machine the server / client is, no matter what kind of GIS software the Web GIS Server uses, due to the use of a general web browser, users can access the Web GIS data transparently, carry out the dynamic combination of distributed components and the collaborative processing and analysis of spatial data on the machine or a server, and realize the sharing of remote heterogeneous data.
3.System costs can be reduced on a large scale#
Ordinary GIS needs to be equipped with expensive professional GIS software for each client, and users often use only some basic functions, which actually causes a great waste. Web GIS usually only needs to use a Web browser (sometimes with some plug-ins) on the client side. The software cost is significantly less than a full set of professional GIS. In addition, maintenance savings due to the simplicity of the client cannot be ignored.
It is necessary to widely promote GIS and make the GIS system accepted by the majority of ordinary users. Rather than being limited to a few professionally trained professional users, it is necessary to reduce the requirements for system operation. A general-purpose web browser is undoubtedly the best choice for reducing operational complexity.
5.Balance efficient computing loads#
Most of the traditional GIS uses the file server structure, and its processing capacity is completely dependent on the client, and the efficiency is low. However, some advanced Web GIS can make full use of network resources, and hand over basic and global processing to the server for execution, while simple operations with a small amount of data are directly completed by the client. This computing mode can flexibly and efficiently seek a reasonable distribution of computing load and network traffic load between the server and the client, and is an ideal optimization mode.
The method of selecting WebGIS development tools#
For developers of WebGIS applications You can comprehensively examine how to choose an appropriate development tool from the following aspects:
This mainly refers to the operating platform of WebGIS on the server side. The server side can be based on Windows NT or UNIX platform, but it is best to be cross-platform or platform-independent. WebGIS products developed based on Java or providing services by CGI usually have this feature.
3.Friendliness of client interaction
4.Data transmission and display technology
For all WebGIS tools, the server-side processing is in vector mode. The grid map and vector map displayed by the client have their own advantages and disadvantages: the grid image client does not need to download any plug-ins or ActiveX controls, but the interactivity is relatively poor; Vector map is just the opposite, but the security of the client is often not very good. Both methods need to adopt some strategy to reduce the bandwidth of map data transmission on the network.
5.Scalable System Architecture
WebGIS applications generally occupy a large amount of system resources of the server. A good WebGIS application should be able to make full use of server resources and have scalability in both horizontal and vertical directions. It can dynamically start the number of services according to the site’s traffic and computing volume, and perform reasonable load balancing among the map application servers.