Database-driven, Web-enabled Public Health GIS Using XHTML, SVG, ECMAScript, DOM and a Three-tier Architecture

SVG Open Conference 2004

Abstract Submission

Gerald I. Cheves, Ph.D. Candidate

Dr. Jason T.L. Wang

Department of Computer Science Department of Computer Science
New Jersey Institute of Technology New Jersey Institute of Technology
University Heights University Heights
Newark, New Jersey 07102 Newark, New Jersey 07102
212 222 4542 973 596 3396

The United States Federal Government has embraced the concept that digital spatial data is a cost-effective capital investment, which benefits many government agencies and other sectors through shared resources after the initial one-time cost of developing the National Spatial Data Infrastructure (NSDI). Under Executive Order 12906 and Office of Management and Budget (OMB) Circular A-16, federal agencies follow the Federal Geographic Data Committee (FGDC) metadata standards for geopspatial data, and are required to make that data available to the public.

Public health will play a vital role in the NSDI, which is being deployed by the FGDC under the aegis of the OMB, because the timely access to public health data is essential for detection, intervention and analysis of adverse human health events. The internet makes the timely delivery of public health data possible by providing immediate access nation-wide via the cable, telephone and wireless communication links that comprise the telecommunications infrastructure. With at least 80-90 percent of all government databases, including public health, containing geo-referenced information, data can be associated with a specific location or place such as area code, latitude and longitude, street address, and many other geopolitical boundaries. Spatial data integration, analysis, and visualization of spatial-temporal events using the Web will increase with advances in technology, such as greater bandwidth to accommodate streaming data and large graphics files, support for spatial databases, and improved software for visualizing spatial data over the web.

In addition to the NSDI, the Geospatial One-Stop initiative by OMB will provide a geographic component for all internet-based government activities across all federal, state and local governments to spatially enable the delivery of government services and eliminate redundancies and their associated costs that are caused by government agencies duplicating geospatial data processing and distribution efforts.

Continued advancement of public health GIS and greater use of spatial data through the internet should be pursued in response to these recent developments.

This model is an attempt to create a data-driven, dynamic thematic map, using a choropleth design that is compatible with OpenGIS* interoperability and XML/GML standards. These two considerations, along with the FGDC, will shape the development of public health GIS through the internet. By using XML (XHTML and SVG), it can incorporate and integrate GML (geography markup language) because XML allows the use of any number of XML dialects within a single document. A map object, or node in the document object model (DOM) can have many child nodes that correspond to the geographical units that are represented in the choropleth map. And they can be accessed with ECMAScript (JavaScript) to create a dynamic map that is data-driven, by updating the color and symbol attributes of the map objects.

In the choropleth thematic map design, data collection units are shaded in intensity proportional to the data values associated with those units, and the shading in this model can be updated from data in a database that resides on a server or DBMS tier of the three-tier architecture. Using ECMAScript, DOM and SVG, the data collection units or geographical units will change shading to correspond to a query on a given disease in a given year.

In general, the client application, which is the web browser, is considered to be a thin client because most of the programming logic resides in the middle tier, but some of the programming logic can be placed in the browser to create a rich client, which is dynamic and fast because the application does not have to load from the server. When data values are passed to the client (browser) from the server, the color is painted on the map with the ECMAScript and SVG.

Common middle tier software consists of a gateway, such as Apache Tomcat, which is the most common, to connect the script in the browser to the program that communicates with the DBMS. Java (Java Server Pages and JDBC or SQLJ) is often used in the middle tier to interact with the DBMS, but ColdFusion, PHP, Perl, and serverside JavaScript, to name a few, can accomplish this task as well.

The advantages of this model over some of the current solutions that involve proprietary software, and other methods that use Java or client-side applications that allow the user to connect to desk-top software over the web, are numerous. An application written in Java is much slower because the applet has to load in the browser. Proprietary software is expensive and is not customizable. In some cases, users may have to purchase software in order to access the GIS resources. Additionally, a link to a desk-top software over the internet requires the user to be conversant enough with the software to build the GIS. SVG only requires a plug-in for the browser, and some browsers, such as Mozilla, are adding the capability to interpret SVG and render the graphics. Response time is fast because this model does not reload updated maps from the webserver upon each new query. Only the colors, shadings and symbols are updated in the browser.

A web-based, thematic map solution for a public health GIS needs to have options, but for the most part has to be automated. The method of determining what range of data values correspond to the grades in shading is one of the major challenges in designing an automated, thematic map GIS. One solution that incorporates some spatial data analysis would be to show statistically significant differences with different shadings.

*OpenGIS Consortium (OGC) is an international industry consortium of more than 250 companies, government agencies and universities participating in a consensus process to develop publicly available interface specifications. OpenGIS(R) Specifications support interoperable solutions that "geo- enable" the Web, wireless and location-based services, and mainstream IT. The specifications empower technology developers to make complex spatial information and services accessible and useful with all kinds of applications. Visit the OGC website at


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