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Flash based WebGIS System and its Application in Monitoring and Evaluating China’s Regional Development Jinqu Zhang, YunQiang Zhu, Juanle Wang, Jiulin Sun, Yuyue Xu

International Journal of Digital Content Technology and its Applications. Volume 5, Number 5, May 2011

Flash based WebGIS System and its Application in Monitoring and

Evaluating China’s Regional Development

Jinqu Zhang1※, 2, YunQiang Zhu2, Juanle Wang2, Jiulin Sun2, Yuyue Xu2 1. Computer School, South China Normal University

2. State Key Lab. of Resources & Environmental Information System，Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences

doi:10.4156/jdcta.vol5.issue5.31

Abstract WebGIS applications are avidly gaining popularity with extensively development and use of GIS

technology. By analyzing the current status of WebGIS, a Flash based WebGIS framework was developed. By converting the traditional GIS files such as ESRI Shapefile to the Shock Wave Flash (SWF) file format, the GIS data was highly compressed and suitable for the Internet publication. The technology was successfully applied to the monitoring and evaluating China’s regional development system. The result shows that flash technology is smart, has easy configuration and fast speed in building WebGIS applications. Flash technology has great potential abilities in expressing spatial information and graphics rendering. To some extent, it’s unique and better than the traditional WebGIS software in graphics dynamic rendering and especially useful for time-series data analysis using an animation method1.

Keywords: Web GIS,Flash SWF, Shapefile

1. Introduction

Geographic Information System (GIS) has come to be an indispensable tool for analyzing and

managing spatial data. The integration of GIS and the WWW has lead to an enormous increase of the usage and accessibility of spatial data. With the advantages in Web Animation, Flash is also suitable for producing maps that are rendered on-the-fly. Flash files are easy to be loaded in the browser and do not need to be stored as pre-rendered files in anticipation of any user request. Thus once a user sends a request, the only work of the software is to paint the objects in a flash file with a particular colour value, which makes it fast. Flash’s excellent performance in manipulating vector graphics and raster images, has long been used to express geographic information. GIS systems developed based on flash technology can be called a FlashGIS system. Seeger (2002) successfully used flash technology in maintaining the image of Iowa beyond the Right-Of-Way. Robin Hilliard (2004) attempts to handle seriously detailed maps in Flash by reading and processing the MapInfo mif/mid files. The Australian Broadcasting Corporation (ABC) news used a simple flash-based GIS system to show the real-time federal elections online in 2004. Zong-zhi Li et al. (2004) discussed the development of WebGIS based on flash. Dang Van Tuyen et al. (2008) designed a flash-based tool and applied it in the management of the Vietnam’s precious forest resources. Some other articles also try to use the flash to show the electronic map. Although there are some WebGIS applications thoroughly flash based, most of them are simple and have limited functionality due to one reason that there is no one tool to convert the existing GIS files, such as Shapefile, directly to the Flash SWF format with attribute data contained. Flash has a good performance in processing vector graphics, but it lacks of the ability in attribute data operation. The manual GIS file format transformation and graphics hand-drawing greatly hinders Flash application in GIS fields, especialy in geographical spatial analysis.

With the development of Internet technology, the term “Rich Internet Applications (RIA)” was put forward in a white paper by Macromedia (now merged into Adobe) in March 2002. Since then interest has been building in the idea of a "rich client": a user interface that is more robust, responsive and

※is the corresponding author and first author.

This paper’s editor is Dr Wang Jian (Chinese Academy of Sciences, [email protected]).

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visually interesting than what can be achieved with HTML (Cameron O'Rourke, 2004). The development of RIA technology provides a new approach that has quickly become the mainstream in developing WebGIS applications. As the largest GIS Corporation, ESRI has released the ArcGIS server application programming interface (API) for JavaScript, Flex and Silverlight one after another for quickly building rich Internet GIS applications. According to the RIA Market Share Penetration and Global Usage, Flash/Flex, AJAX (shorthand for asynchronous JavaScript and XML) and Microsoft Silverlight are the top three most popular RIA frameworks, with penetration rates around 96%, 80% and 44% respectively. The popularity of RIA technology in WebGIS applications also arouses the researchers’ interests. Leonardo et al. (2007) compared several RIA technologies focusing their usage on GIS development and pointed out the rationality of each RIA technology. Adnan et al. (2010) describes different mapping technologies and web application development standards that are relevant to the development of WebGIS applications. Besides ESRI, some other companies such as Google, Yahoo, Microsoft and others, have also released relative maps APIs for use with the Adobe Flex framework. By using of these various APIs, lots of WebGIS systems developed by Adobe ActionScript 3.0 have been applied in various fields. Most of these applications, however, rely on the web services using heavy servers with request/response mode, such as the map services published by the ArcGIS server. A suit of map service software has to be installed firstly, which may be inconvenient and improvident at times.

When developing a WebGIS application, the most important aspect is matching the application to the appropriate technology. In consideration of the excellent idea in RIA and the power ability of Flash in graphics expressing, this paper focuses on the constructing of a vectorWebGIS system based on flash technology. This includes: (1) the method to convert existing Shapefiles to SWF format; (2) WebGIS functions design and development based on Flash SWF map files; (3) the application in monitoring and evaluating of China regional development. This study provides an alternative approach and is helpful to the WebGIS applications.

2. WebGIS development based on Flash technology

2.1 Method to convert existing Shapefiles to SWF format

SWF (originally an abbreviation for "ShockWave Flash") is a file format for multimedia, vector

graphics and ActionScript in the Adobe Flash environment. According to statistics performed by Adobe, Adobe® Flash® Player is the world's most pervasive software platform. It is used by over 2 million professionals, reaching 99.0% of Internet-enabled desktops in mature markets as well as a wide range of devices (Adobe, 2009). Besides superior manipulation of vector and raster graphics, Flash can support bidirectional streaming of audio and video, integrating them into web pages. These characteristics indicate that Flash has good potential for building WebGIS applications.

The main task of WebGIS systems is to publish, process, visualize and analyze spatial data through the Internet. Li Luqun (2002) analyzed the architecture and discovered technologies of common architecture in WebGIS. According to the previous studies, the technology of WebGIS has been very mature with two tier or three tier client/server architecture. Usually, the user sends a request to the server and then the server processes the request and generates a bitmap image returning it to the client screen. This processing flow needs two Internet transfers and lots of server side processes, making the speed of this mode very slow.

In order to quickly build a vector WebGIS system based on Flash technology, the first thing is to convert the traditional GIS files to SWF format with attribute data containing. Currently, flash is known to easily support vector and raster data by transforming geographic coordinates into Flash canvas coordinates. But rarely studies focused on the attribute data management in the SWF file and two methods for supporting attribute data were proposed here.

The first method is to use the component, a new function in Flash software since its version 8.0. The component is a compound body that supports field defining and data storage, in additio GIS data can be supported and integrated in one component. Figure 1 shows a common definition of a component designed in Flash project. Most of the information about a GIS layer file, including coordinate system, projection, scale, attribute data fields and so on, has been included and more fields can be added freely.

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4. Discussion

Simple comparisons of our WebGIS resolution to the ArcGIS server and previous other Flash GIS

applications were performed. Table 3 shows the comparison results.

Table 3. Comparisons of Flash based WebGIS to the ArcGIS server and previous Flash GIS applications

Comparing items Flash based WebGIS ArcGIS server

Previous Flash GIS applications

Map preparation Easy Easy Complex

Map loaded time Fast when SWF file size is smaller than 3M

Slowly Fast when SWF file size is smaller than 3M

Response time for client operation

Fast Slowly Fast

Ability of spatial analysis Weak Strong Weak

Functions extensibility Good Good Good

Complexity of installation Simple Complex Simple

Software and development charge

Cheap Expensive Cheap

According to the comparisons, Flash was approved to be a good technology in developing WebGIS system if the traditional GIS data can be converted to SWF file format with fast speed. The conversion allows GIS data to be easily displayed locally or on the Internet. On the other hand, the Flash SWF file is vector-based and highly compressed, which is much smaller than traditional GIS file such as ESRI Shapefile, making it have a high visit speed and no distortion when zoom in and out. Finally, Flash has very powerful rendering and animation making abilities that make it especially suitable for thematic

Very powerful rendering and animation making abilities that make it especially suitable for thematic map expression with different colours, pictures and patterns.

Flash provides an alternative approach for the WebGIS applications. Although it doesn’t have the powerful functions like ArcGIS server, it has its own advantages. Firstly, the installation is easy and the only requirement is one web server like IIS or Apache tomcat. Secondly, it has faster response speed because the functions and its realization are all performed on the client as long as the SWF map files are completely sent to the browser. Thirdly, it has powerful thematic rendering abilities and can represent the thematic in an animation way. Functions like this have excellent capabilities in expressing GIS information based on time series, which are unique for Flash.

On the other hand, some limitations such as the spatial data analysis and the processing speed for the large SWF map files are inevitable. The functions of the WebGIS based on Flash can be increasingly powerful by continuously development using Actionscript 3.0. The key problem is how to process the large SWF map file because all the graphics are stored in one file which must be transmitted to the client browser completely. When the SWF file size is larger than 3M, the response time becomes slow. To solve this problem, slicing technology can be applied to process the large SWF file. The small sliced SWF file will automatically be amalgamated as one whole. This method can solve the problem to some extent, but if the ESRI shape file is too large, there are still some limitations in loading speed and processing efficiency. In our project, the GeoWebCache (GWC) service published by GeoServer was used to solve the large data file and our Flash based WebGIS integrates the vector SWF map and GWC map in the same window. This resolution solves the problem of large data file and expands the applications of Flash based WebGIS greatly. Another problem is that the client explorer has to install the Adobe Flash Player plug-in so that the SWF file could be viewed. However, it’s not determinant factor because the Adobe Flash Player plug-in can be easily installed online. According to the statistics of Flash Player Version Penetration, it has reached 99% of Internet-enabled desktops in mature markets as well as a wide range of devices.

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5. Conclusion

The application of Flash based WebGIS will be quickly gaining much popularity as its technology

develops. Compare with the traditional WebGIS development method, the development of Flash technology and the arrival of RIA era provide motivation for us to study a new WebGIS approach. According to our study, it is quite suitable to use the Flash based WebGIS approach, taking ESRI Shapefile for example, when every Shapefile sizes in a project is smaller than 20M. This will save costs and allow for quick response speed. If the Shapefile size is larger than 20M, some open source software such as GeoServer or commercial software such as ArcGIS server may be needed for an assistantance.

According to the application in our project, it is approved that Flash based WebGIS is smart, has easy configuration and fast speed, giving it great potential in expressing spatial information. It is different from that of AJAX, Silverlight and even the previous Flex, because all of these RIA frameworks depend on extra GIS servers such as ArcGIS server, and they recur to the API to visit the GIS web services. The Flash based WebGIS is different and it is absolutely vector based without any extra map server. The network support characteristics of SWF file also enable it to apply and develop the service oriented technology in the map publication, and this will integrate the Flash SWF maps with other online map services. With the powerful abilities of Flash Actionscript 3.0, a lot of spatial analysis functions will be supported by Flash based WebGIS system.

6. Acknowledgements

This work was supported by China Postdoctoral Science Foundation (Grant No. 20090460505),

National High-Tech R&D Program of China (Grant No. 2006AA06A306) and Specific environmental nonprofit industry research (Grant No. 200909110). We give great thanks to Dr. David Finn from University of California santa cruz for his grammar corrections for this paper.

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