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2-1 Ubiquitous GIS
In many daily scenarios, users can benefit from some aspects of ubiquitous GIService. They can receive a traffic alert, find the location of a colleague, and search for the closest restaurants [URL 1].

Recently, with the new challenges in the work and life, wired GIS cannot meet the demand of the users in many situations. Eighty percent of the whole information is spatial related data, most of mobile device users tend to access spatial information via wireless network. Wireless GIS is developed under web GIS technology, and there are many similarities between these two. But, wireless GIS has its own characteristics, because of the limitation of the mobile devices and the wireless communication network and technology.

2-2 Wireless Characteristics
As the power of phones, PDAs, and other wireless devices grow, the advent of an entire generation of wireless web is finally materializing outside the labs and professional circles and into the mainstream [Arciniegas, 2001].

Wireless and mobile devices have restrictions and shortcomings that differ from desktop computers in many fundamental ways. Additionally, GIS data to be served usually have large volumes and need modern techniques to be served through mentioned restrictions. Above problems cannot be solved only by providing special interface for handheld device onto conventional GIS [Takino, 2001]. To overcome mentioned obstacles, special architecture must be designed.

2-3 General wireless model
There are several significant features in the wireless model, become evident when it is compared with traditional web model (client/server model).The most important features are, Gateway. In this model, the client does not talk to server directly; and gateway is responsible for this task, also client forwards the request through gateway to final server, Encoding and compression of the data. The data are encoded by gateway to be passed to the client; gateway encodes original server response and sends it to client in compressed format better suited to the restrictions, and Type of content. The data provided by server is not of the same type as it is in the web applications (i.e. it is not HTML); for example data content is marked up in WML (Wireless Markup Language) (Figure 1).


Figure 1: General wireless model
Moreover, wireless GIS adds its particular characteristics to such model. To overcome low device power, thin client architecture must be implemented that takes most of GIS process burden from handheld device to server machine. Moreover, it is expected that busy transaction will occur as a result of frequent request from enormous number of users. A mechanism to resist heavy transaction load is required on server. In applying to practical use, operation management GIS run on workstation will be required. In summary, when realizing mobile GIS, supportive GIS management system based on backend server machine is more required than GIS application itself that is active on mobile device.