外文翻译---在网络地理信息系统环境中地图的作用-环境工程(编辑修改稿)

外文翻译---在网络地理信息系统环境中地图的作用-环境工程(编辑修改稿)内容摘要：

s means that maps to be displayed should load quickly and this puts constraints on the file sizes. Solutions to this problem are discussed later. The Web map has some advantages that are shared with all digital maps. One can zoomin or out, it is possible to pan, while layers can be switched on or off. The map can also be queried. Clicking a symbol can give access to the database behind the map. Simple operation such as measuring distance or areas can be executed. The disadvantages are related to practical usability aspects. Paper maps offer better usage in the field, although recent hardware such as advanced PDA or tablet PC’s offers interesting alternatives. Additionally screen resolution of the often small devices will put extra demands on the design. Even more critical is that uptodate information is expected. In the past, map provision was very much supply driven by cartographers who would consider user needs. Today, rightfully so, one has to consider a demand driven environment and some of the cartographic needs may be solved by algorithms used while creating the maps on demand. 4 Look of the maps What makes Web maps unique? As seen in the previous section the Web as medium to display maps has many interesting advantages, but also some disadvantages. Just scanning paper maps or using default GIS maps and putting them on the Web is not a good alternative. However, in some situations there is no design alternative. Scanning historical maps and publishing them on the Web might be the only solution to make them available for a wider audience, and opening up our cultural and historical heritage. If the above is taken into consideration welldesigned Web maps can be recognised as relatively ‘‘empty’’, . they have a limited map content. This should not be considered as problematic since one can include lots of information behind the map image or individual symbols. Access to this hidden information can be obtained via mouseover techniques or clicking on map symbols (Worm 2020). To ensure this approach one has to make sure the symbols have an appearance that invites clicking them (see Fig. 2). In the case of mouseover techniques the appearance of a symbol will change or textual information appears on the map. Clicking the symbol might open new windows or activate other Web pages. An advantage of those well designed Web maps is that they can be easily used in the world of mobile geoputing. People will have portable devices such as mobile phones and/or personal digital assistants and callin for location based information. Small maps with answers to questions such as how do I get to the railway station, or where is the nearest bookshop will appear on the small screen of these devices which often will have a GPS receiver built in to establish the owners position. The possibilities offered by the Web have extended the traditional cartographic variables as proposed by (Bertin 1967). Web design software enables the application of new variables, like blur, focus, and transparency, Fig. 2. Interactive map displaying Napoleon’s Campaign into Russia design with Flash The user can select the map content and run the animation. During the animation the map background will adapt to the season. See URL2 (Kraak 2020)while shadow and shading play a prominent role as well. Blur gives symbols a fuzzy appearance and can for instance be applied to visualize uncertainty, while focus will introduce blinking symbols to attract attention (DiBiase et al. 1992). Both transparency and shading and/or shadow can be used to simulate a threedimensional look. Transparency can be seen as a kind of fogginess, whereby part of the map content is obscured or faded in favour of other information. For example it can be applied to subdue the background in a map in order to enhance the main theme in the foreground (for instance a drape of geology over terrain features). In a threedimensional ‘‘landscape’’ environment it can also be used as a depth cue. The use of shadow and shading increase the sense of depth. Shading is monly used to increase the contrast between ‘‘figure’’ and ‘‘ground’’ or, for instance in relief maps to create a threedimensional terrain impression. Shadow, also known as cast or drop shadow, can be applied to give the symbols a threedimensional look. In Web maps this threedimensional feel of the symbols invites the user to click on them to activate a hyperlink or mouseover effects. The visual effect of shadow is casting a shadow of the symbol on the background. The origin of these new variables is partly to be found outside cartography (Spence 2020。 Wilkinson 1999). The new variables have been fully accepted in cartography (Kraak and Brown 2020). However, further research on the new variables remains to be done, because despite all technological progress it remains important to make sure that the new representations and interfaces really work. 5 The dissemination of maps The Web is currently the medium to present and disseminate geospatial data and maps. The Web allows one to offer the data and maps platform independently and a virtually unlimited number of users can access the map anywhere at all times. However, there are still many problems to be solved. The performance of working in a WebGIS environment depends on several technological factors. Among these are the inter connection, the traffc intensity, the data effciency, and the capacity of the client and server machines. These days the nature of the task will decide if it will be executed at the client side (the user’s machine) or at the server side (the provider’s machine). Software vendors offer different solutions. Choosing a particular type of solution could tie the user to a particular environment. Another aspect of WebGIS and the current developments around the Geodata Infrastructure。