Vincent Zhuang, John Sun, Matthew Moss, Seth Israel, Bryan McEnaney, and Dave Wolf

The Environmental Protection Agency�s Envirofacts Warehouse Web site is being visited nearly one million times every month via the World Wide Web at http://www.epa.gov/enviro. Envirofacts includes many gigabytes of both spatial and non-spatial data. Online GIS applications, known as Maps On Demand, add a new dimension�visualization�to the information contained in the Warehouse. However, the existing geospatial data database cannot be effectively served for comprehensive Web-based GIS applications; MOD cannot be easily upgraded to produce real-time maps in interactive mode. EnviroMapper, a Web-based interactive GIS application, begins a new generation of MOD. It provides a true, visual path to Envirofacts using the latest technology including the World Wide Web, virtual seamlessness, spatially-enabled Relational Database Management System, and Object Linking and Embedding Component Object Model. The legacy geospatial data were re-engineered and are being moved to an Oracle relational database. EnviroMapper bridges GIS and online queries within the Envirofacts Warehouse. It also delivers information and data in graphic user interface (GUI) that has been widely used in desktop GIS applications. EnviroMapper is a comprehensive visualization tool to the data in the Envirofacts Warehouse. It will also serve as the core component for the upcoming On-Line Analysis Process (OLAP) within Envirofacts.

The Environmental Protection Agency�s (EPA) has built a World Wide Web (WWW) based warehouse, known as the Envirofacts Warehouse. The Envirofacts Warehouse Web site, known as http://www.epa.gov/enviro, is being visited nearly one million times every. The Warehouse allows the public to retrieve environmental information from EPA databases on Superfund sites, drinking water, toxic and air releases, hazardous waste, water discharge permits, and grants information from the Web. It provides online queries and Maps On Demand, which is a suite of Web-based GIS applications including Query Mapper, Facility Density Mapper, SiteInfo, ZipInfo, CountyInfo, and BasinInfo. Online queries permit users to retrieve data while MOD lets users to generate maps.

These Web-based GIS applications produce static maps. In other words, a map is generated in delayed batch mode based on the request. No further manipulation can be performed to the output. The backbone spatial database for these applications was the EPA Spatial Data Library System (ESDLS), which is managed in ArcInfo LIBRARIAN. This type of database cannot be effectively served for Web-based GIS applications. In addition, these applications were written in ArcInfo AML and cannot be easily upgraded to produce dynamic maps via WWW.

The first task of the EnviroMapper project was to re-engineer ESDLS. The second one was to develop a comprehensive Web-based GIS application, called EnviroMapper. EnviroMapper generates real-time maps in interactive fashion. It also executes an Envirofacts query via the HyperText Transfer Protocol (HTTP) and can be invoked by an Envirofacts query in the same way as the existing Query Mapper application.

Data to be serve on the Web need to be compact, if they are flat files, due to the bandwidth of the Internet or managed by a spatially enabled Relational Database Management System (RDBMS). Flat files need to be intelligently indexed for being served via WWW.

ESDLS is a repository for EPA�s new and legacy national geospatial data holdings (Catlin, 1997). It contains nearly 50 gigabytes of spatial data, including the Topologically Integrated Geographic Encoding and Referencing (TIGER) Lines data, the USGS Digital Line Graph data, the USGS Hydrologic Unit Code (HUC) 1:250K regions, subregions, accounting units, and cataloging units, and locational coordinates for the EPA-regulated facilities contained in its programmatic databases. The geospatial data stored in ESDLS cover the conterminous United States, Alaska, Hawaii, Puerto Rico, and the Virgin Islands (Catlin, 1997).

The ultimate goals of re-engineering ESDLS are to move all geospatial data to an Oracle relational database in which the Envirofacts Warehouse resides and to manage them with a spatially enabled RDBMS. An intermediate product was the EPA national shapefile repository.

The EPA national shapefile repository contains four types of data: Streets 4.0 from Wessex, Inc. in Winnetka, Illinois, National Transportation Atlas Databases 1997 from the Bureau of Transportation Statistics of the U.S. Department of Transportation (DOT), ESDLS, and Dynamap ZIP Boundary File v6.0 from Geographic Data Technology, Inc. in Lebanon, New Hampshire. Wessex data, the ESDLS Envirofacts points, and the DOT railroads and major roads were assembled by national, state and county dimensions; ESDLS Hydrologic Cataloging Units and River Reach File 1 data were assembled by four-digit HUC subregions; and GDT�s five-digit Zip code boundary data were assembled by the first two-digits of the 5-digit Zip codes. The shapefile database is scale dependent (Table 1). The criterion for tiling data layers in this way was that a shapefile cannot be greater than 15 MB when being served via the Internet.

Although the shapefile database was tiled by political, hydrologic and Zip code boundaries, it is virtually seamless within the entire geographic extent. The seamlessness was provided by the virtual grids cross-referenced to states, counties, catalog units, and Zip codes (Sun, et. al., 1998). Using virtual gridding eliminated the need to load data for more than three-thousand counties at once in an application of national scope. Given a zoom-in window, for example, those counties that fall in this window can be intelligently identified and the corresponding layers can be automatically loaded into memory. This virtual seamlessness makes Web-based geographic data access feasible and efficient via application such as EnviroMapper.

EnviroMapper is a Web-based GIS application that includes an HyperText Markup Language (HTML) based client interface and a server-side mapping engine. It is a visualization tool for the EPA national shapefile repository. It also provides a user-friendly search tool for the Envirofacts Warehouse.

One of the requirements for EnviroMapper was that it needed to be able to run with a 16- or 32-bit Web browser, such as Netscape 2.x, Internet Explorer 3.x, or later. This requirement limited usage of Java language (Sun Microsystems, Inc.) in the development of the EnviroMapper client interface. The interface was developed in HTML and JavaScript, which are compatible with the Web browsers mentioned above.

Three HTML frames were used for the EnviroMapper banner, toolbar, and map display, respectively. The banner was designed to identify EnviroMapper. The toolbar was developed to have similar look-and-feel and manipulation capabilities to that available in ArcView or Java-based Map Café (Figure 1). Seven icon buttons were designed for the toolbar, each having a quick tip (Qtip) message displayed next to the button or on the browser window status bar (at the bottom of the browser) to show its function.

Figure 2. EnviroMapper with the county level data displayed.

The frame holding map display was configured in three columns, with Legend on the left, Main Map Display in the middle, and Locator Map Display on the right. There are two buttons associated with each legend: a toggle button (in circle) for query selection and a checkbox (in square) for layer selection. There is also a symbol to identify color and type of shape. At the bottom of this column, a checkbox was designed for the Locator Map selection. All toggle buttons and checkboxes are HTML form objects. The map will be displayed in the Main Map Display. The Locator map and single feature identification result will be displayed in the Locator Map Display underneath the Locator map.

The mapping engine was developed with MapObjects Version 1.2 and MapObjects Internet Map Server (IMS) Version 1.0 under Visual Basic Version 5.0 environment. MapObjects is Object Linking and Embedding Custom Controls (OCX) and developed by Esri. The mapping engine first parses the request submitted from the client, generates a map and/or query results based on the processed request, and publishes them back to the client. Thus, it is a server-side mapping engine (Zhuang, 1997). The engine is composed of a collection of modules, with each corresponding to a button on the toolbar of the client interface.

Each map generated by a MapObjects application is a gif or JPeg file; query results are presented in HTML text. Therefore, no map needs to be generated until a gif/JPeg request is submitted from the Web browser. This indicates that there are two steps to produce a map via WWW using MapObjects and MapObjects IMS. The first one is to publish HTML with all parameters required; the second one is to generate map based on those parameters. EnviroMapper stores all parameters needed to draw a map on the client so that each of maps can be generated independently.

HTML 3.0 and JavaScript 1.0 were used to develop the client interface. Although JavaScript Versions 1.1 and 1.2 have more advanced features, Internet Explorer 3.x does not support them. Netscape and Internet Explorer specific extensions were not used in EnviroMapper.

Visual Basic 5.0 was the primary programming language used in the development of the EnviroMapper mapping engine. EnviroMapper took advantage of object-oriented programming available in Visual Basic 5.0. Practical Extraction and Report Language (Perl) was also used to develop a function that generates a county list based on a chosen state. Perl is more practical and effective for text extraction than Visual Basic.

EnviroMapper presents the EPA national shapefile repository in three different levels: national, state, and county. Switching from one level to another is done automatically by the mapping engine. A user can check on/off any layer available at that level. After the selection, he can click on the Redraw button to refresh the map. A user can also do feature identification layer by layer. If the current theme is Envirofacts points, the user can launch the Envirofacts search engine on the identified site. EnviroMapper provides Zoom-in, Zoom-out, Pan, Identify, and Query. Zoom-in can be by scalar, radius, state, county or Zip code. Scalars or radii are available through a pulldown list; states or counties can be selected from a listbox. If a user selects a scalar or radius and then clicks on the map, the map will be zoomed in by the chosen factor at the center of the clicked point; if he chooses a state or county or type in a Zip code, the map will be zoomed in to the specified geographic extent. A zoomed window can be reset by clicking on the Zoom Reset button. A query on multiple Envirofacts points can be launched by clicking on the Query button. All queries are executed via the Envirofacts Warehouse search engines. EnviroMapper also provides a Locator map that shows the relative position of current main map window.

The EnviroMapper mapping engine runs under Microsoft Windows NT 4.0 on a 200 MHz (single CPU). The machines was configured as 50 GB hard disk, 256 MB RAM, Super VGA with 8 MB VRAM. The Web server was Microsoft Information Internet Server (IIS) Version 3.0.

With the aid of commercial datasets, the EnviroMapper project has achieved its initial goal to re-engineer ESDLS in a relative short period of time. Although the data were tiled by boundary, they can be accessed seamlessly using virtual grids. With virtual grid in place, an existing boundary-based GIS database can be served via WWW without any changes. Virtual seamlessness is a feasible solution to small or medium geospatial databases (Sun, et. al., 1998). The EPA national shapefile repository is being moved to an Oracle database. It will be managed together with the Envirofacts Warehouse by a spatially enabled RDBMS. In other words, EPA national geospatial data repository will be part of the Envirofacts Warehouse. Virtual seamlessness will be upgraded to physical seamlessness once the Warehouse RDBMS is spatially enabled.

As a new generation for GIS, EnviroMapper provides a comprehensive Web-based mapping in interactive fashion. It is a visualization tool for the Envirofacts Warehouse and a user-friendly search tool for the Envirofacts Warehouse as well. EnviroMapper can be run with Netscape version 2.x, Internet Explorer version 3.x, or later. It has been proved that a server-side mapping engine can be used to serve a national scope of geospatial databases that contain information at the county level.

The authors gratefully acknowledge Theresa Urban and Nikki Dermentzis for their review. This work was supported by the EPA Office of Information Resources Management Mission Oriented Systems Support contract under the Envirofacts Information Warehouse Initiative delivery order (DO #91).

Vincent Zhuang

Science Applications International Corporation

200 N. Glebe Road, Suite 300

Arlington, VA 22203

John Sun

Science Applications International Corporation

200 N. Glebe Road, Suite 300

Arlington, VA 22203

Matthew Moss

Science Applications International Corporation

200 N. Glebe Road, Suite 300

Arlington, VA 22203

Seth Israel

Science Applications International Corporation

200 N. Glebe Road, Suite 300

Arlington, VA 22203

Bryan McEnaney

Indus Corporation

1953 Gallows Road, Suite 300

Vienna, VA 22182

Dave Wolf

Environmental Protection Agency

401 M Street, SW

Washington, D.C. 20460