The basic concept of WebGIS
Geographic Information System GIS
With the development of technologies such as computers, networks and databases, and the deepening of applications, the development of Geographic Information System (GIS) technology presents new features and trends. Internet-based WebGIS is one of them. In addition to the traditional government, real estate, resources, environment and other government management fields, WebGIS is also promoting the rapid development of industries, such as car navigation, mobile location services, intelligent transportation, disaster relief, urban facility management, modern logistics and big data analysis that are closely related to the lives of ordinary people.
With the rapid development and widespread use of the internet, people's demand for geographic information systems is also growing. Internet has become a new GIS operation platform, WebGIS (Network Geographic Information System) formed by its integration with GIS is the inevitable development trend of GIS software. WebGIS has also become a tool for the public. At present, there are three main modes of network technology application in GIS: centralized mode, C/S mode and B/S mode, among them, WebGIS based on B/S mode is a new mode to solve C/S mode, the problems faced by WebGIS and meeting the needs of users for information management.
The full name of GIS is Geographic Information System. It is a technical system for collecting, storing, managing, computing, analyzing, displaying and describing geographically distributed data in all or part of the Earth's surface (including the atmosphere) with the support of computer hardware and software systems. Since Roger Tomlinson, the father of GIS in the 1960s, created the acronym GIS (Geographic Information System), the field has changed dramatically. Nowadays, students can encounter many of the same basic contents in related courses such as “Geographic Information Science”, “Surveying and Mapping” and “Space Information System”. The G in GIS has been interpreted as "global" and "geospatial" rather than the original "geographic"; S is not the original "system", it is “science”, “services” and “studies.” However, if you want to find a word to describe the commonality of all of these things, “geospatial” may be the best option.
The most easy-to-understand explanation is that GIS uses maps to generate paper maps or generates images by aerial photography and satellite shooting, which is stored in a computer, displayed in the form of a map or a picture, then, according to the actual needs of production, provide life and scientific research, specific processed data.
Internet technology development
The World Wide Web has changed all aspects of human society and has changed the geographic information system. The convergence of the World Wide Web and geographic information systems has created an emerging field of the World Wide Web Geographic Information System (WebGIS). Web GIS has developed rapidly since its appearance in 1993, and its unique use and charm have become one of the main attractions of people using the Internet.
The tremendous impact of the World Wide Web and its wide connectivity have benefited GIS, leaving GIS out of offices and laboratories.In the computers that reach thousands of households, and reach hundreds of millions of public mobile phones, GIS is widely used in government, business, education and scientific research, 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 where they are, is critical to making the right decisions. GIS (geographic information system or geographic information science) is a technology and science that can handle the collection, storage, management, analysis, expression and sharing of geographic data to help people make the right decisions.
Geographic Information Systems emerged earlier than the Internet. In 1962, Roger Tomlinson developed the world's first operational geographic information system for the Canadian Federal Ministry of Forestry and Agricultural Development, called the Canadian Geographic Information System, which is used in detailed survey, statistics and planning for land use in Canada.
Roger Tomlinson pioneered GIS and is committed to advancing the development of GIS methodology (Tomlinson, 2011) and is therefore known as the "father of geographic information systems."
Although GIS is often used to compile maps, its functionality is far from limited. It has powerful analysis capabilities that can link many seemingly unrelated data based on their common geographic location and enable comprehensive analysis, excavate relationships, rules, and trends that are hidden or not easily displayed in spreadsheets or statistical software packages to support people making scientific decisions. GIS can abstract the real world into a series of spatial data layers, such as land use, elevation, images, neighborhoods, roads, and commercial customers. GIS can combine these layers in a variety of ways and draw them into a variety of thematic maps. Moreover, GIS can further analyze these layers and extract a lot of useful information to solve the following problems:
In the past few decades, the development and application of GIS has benefited a lot in many fields. The emergence of the World Wide Web has provided a broader stage for GIS, allowing GIS to go to more industries and enter thousands of households.
What is WebGIS.
Before giving a clear definition to WebGIS, it is necessary to distinguish between several related concepts: network GIS, Internet GIS or Internet GIS and World Wide Web GIS (WebGIS). WebGIS is often called Web Mapping in foreign countries. ). Differentiating these concepts will help to correctly understand and apply WebGIS.
The network here includes local area networks, wide area networks, the Internet, and various wireless networks. The protocols used by network GIS can be either TCP/IP or other layers of protocols such as HTTP, WAP, GPRS, and Bluetooth protocols.
Internet GIS is a subset of network GIS, which is a network GIS based on TCP/IP protocol, so it can be deployed to run on the Internet. These GISs can be either C/S mode or B/S mode, Google's Google Earth software is a client software for the C/S mode web map service provided by Google.
Therefore, WebGIS is a B/S mode distributed computer application system for storing, managing, analyzing, publishing and sharing geographic information based on the HTTP protocol in the Internet or Intranet environment.
WebGIS can be regarded as a subset of network GIS and Internet GIS, meanwhile, it is a distributed GIS built on higher-level application protocols, which is a technically more complex network GIS, on its server side, other distributed computing models are often used due to tasks such as load balancing.
Since the beginning in the 1980s, a large number of GIS software has appeared in the C/S architecture, which means that professional GIS software needs to 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, and the ability to do more complex functions and respond quickly. But at the same time, its shortcomings cannot be ignored. First and foremost is the inconvenience of promotion, and the reason for the inconvenience is that the C/S system has its own natural disadvantages: it is not convenient to update, it is not convenient for cross-platform, and it is not convenient for users to use without installing the specified client.
Since the beginning of this century, the Internet has entered an explosive growth stage, and the laying of the network and the increase of the network speed have increased substantially, which provides a solid environment for the development of WebGIS. As a result, more and more B/S-based GIS systems are beginning to provide services, and in the emergence and maturity of RIA (rich client) technology and AJAX (dynamic web page) technology, WebGIS can basically display the same effects and features as C/S. The great development of WebGIS is 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 to present the functions provided by the GIS discipline to the user with B/S technology, so that users only need to use one of these GIS functions in the browser.
Basic characteristics of WebGIS
Web GIS can be simply defined as a GIS based on the Web environment. At present, Internet/Intranet is rapidly expanding at an alarming rate, under such circumstances, how to introduce GIS into the Internet/Intranet world and make GIS fully utilize and utilize the advantages of the Internet has become an important topic in GIS development research.
From the perspective of system integration, integrating OpenGIS, ESR, and Intergraph, Web-based GIS 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 multiple sources, multiple levels of scale, and geographic data stored in different locations; It can be integrated with non-GIS systems (such as Delphi) through technical means such as object management, middleware and plug-ins; It can run collaboratively across platforms through technologies such as Java, CORBA, and DCOM, and supports client/server mode. Open systems benefit GIS users, software developers, and system integrators. Second, Web GIS is suitable for running in a World Wide Web environment. Integrate GIS software with Web server, through ordinary browser, users can manipulate network GIS anywhere and enjoy geospatial information service, thus expanding GIS into public service system; At the same time, it will broaden the map publishing channels, reduce the cost of data distribution, and increase the 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 directory services, geographic data access services, geospatial analysis services, geographic model system services, and geospatial visualization services. Through interoperability technology, a GIS process can be coordinated by multiple GIS servers, they share distributed data objects and work together on multiple different platforms to maximize the use of network resources.
The composition of WebGIS
To understand the concept of WebGIS, you need to 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 that consists 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. It may be a server on the Internet or a cloud computing center. Sometimes both the server and the client can be installed on the same computer, but logically they are still two separate units.
A single WebGIS is typically a three-tier architecture, including a data layer, a logical layer (or middle layer), and a client (or presentation layer). With the popularity of geo-aggregation (see Chapter 4) methods, a WebGIS often utilizes one or more WebGIS services to form an n-layer 3 >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, also incorporates WebGIS functionality and can be used as a client for WebGIS. For example, you can use ArcGIS Online, the US Geological Survey, Microsoft Bing Maps, or other basemaps provided in ArcMap without having to purchase and install these basemap data yourself.
Geographic information systems are 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. By the 1980s and early 1990s, these components were often installed on different computers on the same LAN, and they could form distributed geographic information systems in different rooms of a building or in multiple buildings. In WebGIS, these components are further separated, and the client and server can be on each side. With the advent of technologies such as Web services and mashups (see Chapter 4), one client can use the data of one server and the analytics of another, which further separates the components of GIS.
The 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 over HTTP;
The geographic information system establishes a mathematical model for surface information, and uses computer technology to store, process, and analyze data. The geographic information system using Web technology is WebGIS. The key features of WebGIS are object-oriented, distributed, and interoperable. It encapsulates GIS data and functionality into objects, and these objects support distributed computing and can be stored on different servers; Objects can be easily exchanged and interacted through a consistent communication protocol.
WebGIS, or World Wide Web GIS, is a B/S mode Internet GIS. 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 general-purpose web browser such as IE, Firefox, etc.
The user interacts with the map through a web browser.
WebGIS is a distributed GIS based on the B/S mode of the HTTP protocol.
It uses HTTP protocol to communicate between browser and Web server. Users send requests to Web server through Web browser, servers usually return interactive HTML or XML format documents, document fragments or other formats of geographical data to users.
Advantages of WebGIS
Compared to traditional desktop or LAN-based GIS, Web GIS has the following advantages:
A wider range of access.
Customers can access the latest data on multiple servers in different locations at the same time, and this unique Internet/Intranet advantage greatly facilitates GIS data management, making data management and synthesis of distributed multi-data sources easier to implement.
Regardless of the server/client machine, regardless of the GIS software used by the Web GIS server, users can transparently access Web GIS data and distribute it on the local machine or a server, because of the use of a common Web browser, dynamic combination of components and collaborative processing and analysis of spatial data to achieve remote heterogeneous data sharing.
System costs can be reduced on a large scale.
Ordinary GIS is equipped with expensive professional GIS software on each client, and users often use only some of the most basic functions, which actually causes great waste. Web GIS usually only needs to use a web browser on the client side (sometimes add some plugins). Its software cost is significantly more cost-effective than a full set of professional GIS. In addition, the maintenance costs saved due to the simplicity of the client cannot be ignored.
It is necessary to widely promote GIS, so that the GIS system is accepted by the general public, and not limited to a few professional users who have received professional training, it is necessary to reduce the requirements for system operation. A versatile web browser is undoubtedly the best choice for reducing operational complexity.
Balance efficient computing loads.
Traditional GIS mostly uses the processing of file server structure, and its processing power is completely dependent on the client, which is less efficient. Today's advanced Web GIS can make full use of network resources, and the basic and global processing is performed by the server, while the simple operation of small amount of data is directly performed by the client. This kind of computing mode can be flexible and efficient to find the reasonable distribution of computing load and network traffic load on the server side and the client side with an ideal optimization mode.