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GeoWorld September 2012

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Open-Source GIS The task was to import the data into tables in a relational database and divide the data-segment table by geographic entities to facilitate queries, joins and other data manipulations. PostgreSQL proved itself to be more than sufficient in handling such tasks. For example, the ACS dataset was broken down into 118 segments. For each segment, there was an Excel template that defined the data columns; the actual data for each segment were stored in two comma- delimited text files: one for census tract and block group, and another for other geographical entities. Manually loading data into an Excel template would entail at least 236 (118 * 2) repetitive moves, not to mention the additional efforts involved to import the data into a relational DBMS. Fortunately, Python can easily be added as a PL/Python extension into PostgreSQL to manipulate Excel files inside the data- base. Through procedure language, rules and trigger functions in PostgreSQL, these otherwise tedious and time-consuming tasks are highly automated and reduced to a couple mouse clicks. Hands-on experiences such as this demonstrated the potential of PostgreSQL and, most importantly, staff's ability to handle the tool, helping reach the critical decision of using PostgreSQL as the database backend to support a large part of geospatial func- tionalities and Web-GIS development at VTA. What really changed the perception of PostgreSQL were a few sample Web GIS applications built on top of this database backend. Map-Server and Web-Client Applications To support Web-map application development, POSTGIS, itself an open-source program, was added to PostgreSQL, serving as a spatial extension that enables a wide range of functionalities. Then MapServer, an open-source platform, was enlisted to generate Web services from geospatial data and drive interactive Web-mapping applications. As a wrapper around MapServer, another open- source program, Fusion, was used as the Web-client viewer application. Besides cost efficiency, the main rationales for choosing MapServer and Fusion for Web- GIS development were the following: —Due to an active online development community, PostgreSQL has a frequently updated schedule, about once every quarter. It would be difficult for other software to catch up with such a frequent updating schedule. Surprisingly, MapServer and Fusion can be easily integrated with the latest version of PostgreSQL to take advantage of the improved performance and functionality. Such easy integration is partly attributed to the software's open nature. For example, to make the latest version of Fusion work with MapServer, a basic debugging tool identifies the few lines of code that went wrong and fixes them. —Flexibility and productivity are like Kate and Edith; it's difficult to have them both. ArcGIS Server and an ArcGIS Server-based Web-client viewer application, by providing a free and configurable devel- opment platform, turn Web-map application develop- ment into a highly effective and autonomous mass production. It also allows a certain level of customiza- tion, such as "mix and match" of widgets to change the Web site's look and feel, but it's basically a "one size fits all" solution. This opens up business opportunities for consul- tants to provide Web-client viewer applications tailored to specific build, needs, taste or idiosyncrasy. However, the service provided by consultants isn't free, and the source code behind customized solutions typically is proprietary intellectual property, not open to intellectual poking or tampering. With the flexibility to configure the frontend application as well as change behavior of the widgets or extend existing functionality, an open- source Web-client viewer application, like Fusion for MapServer, seemed more suitable. 20 W ORLD / SEPTEMBER Deliverables Deliverables include Web-service layers and Web-map applications. Currently, VTA's Web-service layers are the building blocks for the internal Web-map applica- tion development, which will be shared with the online development community and the general public to encourage citizen participation, coordination and col- laboration in future planning processes.

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