Home Articles Studies on the Key Technology of Spatial Data Sharing on the Internet

Studies on the Key Technology of Spatial Data Sharing on the Internet

Wang Lei, Chi Tianhe, Zhou Xu, Chen Huabin, He Jianbang
Institute of Geographic Sciences and Natural Resources Research,
CAS, Beijing 100101,ChinaM
Email : [email protected]

1 Introduction
China’s Sustainable Development Information Sharing System is a spatial data management and analysis system that possesses the base functions of webGIS. Chinese sustainable development information can be accessed through this system. These data include information of vegetation and animals resources, microbe species, crop species, forest, land use, nature protected area, geology and mineral resources, ocean resources and environment, climate and integrated information of disasters. All these data can be queried and accessed through many approach, some basic analysis and professional analysis function are also supplied.

2 System concept design
China’s Sustainable Development Information Sharing System makes fully use of the quick development technology of Internet, combing many new technologies such as webGIS, Web database, metadata, network dynamic model Fig 1 is the frame structure of China’s Sustainable Development Information Sharing System.

Figure 1 The Frame Structure of China’s Sustainable Development Information Sharing System
This model includes user tier, server tier, data tier, network tier, technology tier and management tier etc. They connect with each other,integrating as a whole.

Users can access this system through user tier. From users perspective,this system is a information serving institute,website can be visited through Internet,information can be browsed by personal manner,free download or with some charge.

Server tier can supply advanced service to users, including information query, data download, dynamic operation model etc. Server tier is set up on data tier,it also can support user tier. It is mainly represented as an integrated software system combing with nertwork, data and hardware. In order to better make use of the data on server tire, some advanced technologies were taken, such as WebGIS technology, metadata technology etc.

Data tier is the core of this system. This value of this system was decided by the practicality, integration, precision and the dynamic update ability of this system. The data in this system is authority data including resource, environment and disaster;It is a distributed database in which data is distributed in network center and network sub-center. All database have a characteristic of spatially referenced earth, and can be display on the map.

Network tier is a virtual network that is organized together through common management, common technology and common user face based on the Internet. It connects all parts of this system together, users can visit this system through Internet.

Technology tier cross both above four tiers, it makes use of all kinds of technology, ensuring the realization of system goal. In one hand, this system make use of present matured technologies,such as Internet, database, Web technology etc ; On the other hand, a series of key technologies need to be solved,these technologies integrate with above four tiers,making system realization possible. In network tier, it is required to ensure the connection between network center and sub-center. It also is required to ensure the internet security;In data tier,it is required to finish former database’ alteration and build a distributed database system;In server tier,it is required to develop client and server software,integrating with all kinds of business software;In user tier,it is required to build a web main page,communicated effectively with users.

Management tier has tight connection with former five tiers,it is the guarantee of system realization and operation normally. During system construction period,management tier need to harmonize with each other. After system construction,it need to ensure it is a self-sustain, normally operate system.

3 System Basic Structure
Based on the system design objective and present information sharing status in China, this system adopts the principle of both centralizing and distributed. Some information is shared in network center, others are shared to serve for public on sub-center, among those the network center is the core of this system, which is made up of three servers, including Web Server, data server and GIS server.

3.1 Web Server
Web Server is the information exchange center between users and application server, it is in charge of receiving user request, returning part information, or hand out this request to those application procedure running at background, it also is in charge of returning the running result as proper form to explorer at HTML/HTTP standard.

Figure 2 The basic structure of system
3.2 Database Server
Database Server is used to manage those sharing database in this system, it can supply needed data for application server and database server.

3.3 Application Srver
Application Server is made up of advanced server which has the ability of fast processing, it also is equipped with the software such as ESRI ArcINFO?Mapobjects and some spatial data processing and analysis software. Application server is the core of this system, it organizes, analyzes and manages those data and information in database and response with the request from users.

3.4 Network Structure
This system is a distributed network. It is made up of network center and sub-center in Beijing, Tianjing and Nanjin, all these are connected through Internet. These nodes also connect with CERNET, CSTNET, CHINAGBN and CHINANET. Yet by logic it is a virtual network on the Internet, all database in network center and sub-center are connected, forming an integer, serving for public as a whole.

4 Key Technology studies

4.1 Client-Server Information Transmission Protocol
In order to realize the information exchange between client and server,a set of information transmission protocol need to be set up. Protocol is composed of request and response. Protocol content need fully reflect system function and some control process. So, system function needs to be clearly defined. From the analysis of system function,we can classify these function as data request, query, analysis, help, control and metadata. Every protocol’ structure is clearly defined. This protocol adopts orientate-object thinking,making the progress of information exchange abstract as the progress of sending information and receiving information. Both client and server act as request-driving.

When a request-object was formed,the request-object was in charge of forming a response-object, then the response-object will finish process automatically. Such a process is same both in client and server, the only difference lie in the different response-object. For example, as for browser,whole request and response progress at server is transparent,it has a message-processing center,which form request, send request and acquire response according to user request.

4.2 Spatial Information Presentation and Integrating Analysis
The presentation of spatial information includes vector and grid two forms. In this system, we adopt the way that combing vector and grid. As for normal information query, explore, users can operate very easily as they are operating desktop. When it concerns with the calculating analysis of data,it need the help of porosity server to decide adopting which way. So, for all registered system model, the describing information need to be supply. Users can make spatial query or attribute query by their way,query result can be display by map or chart. For those statistic data that can be used to make thematic, it can supply making-chart tool, users can make style and position setting, such as legend, map name, map symbol , color,so they can make full understanding of the information they acquire.

The analysis function in this system includes spatial analysis and statistic analysis. Spatial analysis concerns with more spatial operation, which can be finished by GIS server. The problem mainly lie in two aspects:One is how to embed the spatial analysis function from other special GIS software into this system, the other is how can present model be shared among users? As for the first question, we use the interface supplied by manufacture factory to use corresponding module or directly obtain the data after analysis. As for the second question, such a question can be solved by establish a set of interface mechanism, and model is requires to embed into system operation with the least change, the future extension should be supplied. As for statistical analysis, many analysis tools are supplied to users, they can use such tools to make statistical analysis aiming at a specific variable.

4.3 WebGIS technology and strategy in development of system

4.3.1 The Strategy of Giving Attention to Both Client and Server
In WebGIS, only emphasizing particularly on server and client both have their weakness. Thus this system adopt a synthesizing development strategy, which give attention to both advantage and potential of client and server, reasonably distribute the burden of operation and transmission, sharing the operation capacity, making this system best.

In order to implement synthesizing strategy mention above, the best way is supplying a intellectualized task-distribute function, which make system automatically distribute the task of data processing according to the operation capacity of server and client. But according to current technology level, it is hard to implement such a goal. This system carry out this function by such a way: at first, the data process task or the information serving function is divided into several distinct task-units; then the possible condition of server and client is classified; last we can put forward a task-distribute project according to every classify. Thus when the system operates, it will judge the combination classify of server-client capacity, and decide the task-distribute project.

4.3.2 The WebGIS Client Development Technology based on Java Applet
Web GIS is a typical application system based on Internet. The client of this system was implemented by Java Applet. Java Applet is a little program that runs on the client, which has all advantage of Java, the best of it is it’s strong ability with system. It is embed in web page through HTML, and sent to the computer of user, and then operated by Internet explorer, which greatly improve the information management capacity on the Internet explorer. This system made use of Java Applet, develop a WebGIS explorer based on image-user interface. Users can easily zoom in, zoom out, pan, identify, make thematic map, legend etc.

4.3.3 The WebGIS Server Development Technology based on MapObject(MO)
MO is a WebGIS OCX developed by ESRI, which can be developed by application developer. In this system we make use of VB, MO and MO IMS to develop a program which can receive the request of GET and POST from client, user can make use of this system to easily browse, manage and release dynamic China’s Sustainable Development Information. The server program begin to run when it receive a request from client, client can transform parameter to this program, server response to this request and process with the order and parameter. As the process finished, the processing result will be transformed to client as GIF format. Such mode has much advantage at present considering the slow speed of Internet transmission.

5 Couclusions
Through the construction practice of China’s Sustainable Development Information Sharing System, it is found that the realization of spatial information sharing for public is in great need and possible, though it concerns with many questions such as policy, standard and technologies. This paper talks about some key technology and has put these technologies into the construction practice of China’s Sustainable Development Information Sharing System .Yet there still lie in many problems need to be solved, such as the integration of mathematics model and GIS technology, the Internet application of sustainable development model, spatial index of large amount of spatial information etc.


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