2-The Key to the Present Is the Past

The Key to the Present Is the Past
Continued...

The fifth design element called for providing preset selections of image layers. Ortho Viewer provides most recent, oldest, and categories that make it easy to select a group of images quickly.

The sixth design element stressed simplified map navigation. Although GIS is becoming more common, Ortho Viewer's designers wanted the application accessible to everyone so the only buttons provided are zoom in, zoom out, pan, and full extent.

Using geographic data effectively demands an understanding of its associated metadata. Where did this data come from? What is its accuracy? The imagery layers have metadata. Ortho Viewer needed to provide easily understood, concise metadata. Information on date flown, flight height, focal length of the camera, pixel size, terrain model, and positional accuracy was chosen for inclusion in Ortho Viewer's metadata.

Finally, although it is great to look at images online, the current generation also likes to print and save the images. Ortho Viewer needed to print and save to common file formats, such as PDF, JPEG, and PNG, that print and save good-looking cartographic products.

Developing Prototypes

After coming up with the design elements, the designers created three prototype user interfaces. These prototypes varied with the size of the small multiples and the enlarged view. The prototypes were well received by representatives from several county departments who provided excellent feedback and identified which departments and divisions would use this targeted tool. In the end, they selected the second prototype.

The Ortho Viewer Development Process

The Ortho Viewer application, designed from the second prototype, consists of four map windows. The map windows are ordered along a timeline starting at the top left with the earliest image and continuing to the bottom right with the most recent. Each map window allows interactive zooming and panning. Zooming in and out can either use the click method to zoom in or out a set distance or a rubber band method that allows the user to draw a rectangle. Panning uses an intuitive drag-and-drop method.

Layers selection is filtered by geographic extent and preset categories make it easy to select layers.

Development was jump-started by using an Esri site starter for ColdFusion MX. From a system point of view, Ortho Viewer consists of an ArcIMS mapping server, an ArcSDE geodatabase, and a ColdFusion MX application server. All of the image layers were loaded into an ArcSDE geodatabase that runs on Microsoft SQL Server. The ArcIMS map service runs on an IBM blade server running ArcIMS 9 and exclusively uses SDE layers for performance. The map service is set with a complicated suite of group renderers with scale-dependent thresholds.

The Web application runs on ColdFusion MX and uses the Mach-II framework for a clean and maintainable software architecture. The business logic is coded in reusable ColdFusion components. The Esri Java Connector is used by the ColdFusion MX application server to communicate with the ArcIMS mapping server.

ColdFusion MX runs as a Java server so integration between the Esri Java Connector and ColdFusion has been easy and rewarding. From a development point of view, the Ortho Viewer Web application uses ColdFusion, Java, JavaScript, HTML, CSS, ArcXML, XML, XSLT, and SQL.

Ortho Viewer gives the user four ways to quickly and easily find a location. The address dialog box uses the ArcIMS Java Connector to geocode addresses and intersections on the fly. The parcel dialog box provides a quick search by parcel number. The places of interest dialog box uses the USGS place-name dataset to give users a quick search by keyword. Finally, the bookmarks dialog box gives frequent users a way to store favorite locations to their computer using cookies. Ortho Viewer makes it easy to turn layers on and off, but for performance reasons, only four layers can be checked on at a time. Preset categories make it easy to select layers quickly.

Metadata is necessary for effectively using GIS data. Clicking on a layer's name in Ortho Viewer invokes the metadata for that layer. Users can also compare the metadata for every layer shown by clicking the Compare Metadata button below the layer list.

Ortho Viewer saves PDF files for printing and archiving using the open source Apache Formatting Objects Processor (FOP) Java library. Apache FOP takes an XML file and transforms it into a PDF file using an XSLT style sheet. Ortho Viewer can also save to a JPEG and PNG by using Java 2D technology, which allows the application server to dynamically generate images in memory.

Conclusion

The Ortho Viewer is an intranet Web application that Pierce County designed to view temporal changes in imagery. The viewer allows users to explore multiple years of imagery for locations throughout the county. This description of the process required to design the Ortho Viewer underlined the importance of focusing on a specific problem and using design elements to make an application more intuitive and user-friendly. It also illustrated that many servers and languages are typically needed to implement a GIS on the Web. For more information, contact

Jared Erickson
Pierce County GIS
950 Fawcett
Tacoma, Washington 98402
Tel.: 253-798-3455
E-mail: jericks@co.pierce.wa.us

About the Author

Jared Erickson is a GIS Certified Professional (GISP) who has worked for Pierce County, Washington's Information Technology department for six years. An archaeologist by training, he specializes in application development of spatially enabled Web sites.

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