Making GIS Databases More Accessible
Apollo Teng, GIS Manager
Montgomery County, Maryland
The Montgomery County Map Room on the Net
With the availability of GIS-based web posting applications such as ArcView Internet Map Server (AV-IMS), one no longer needs to rely on more ‘expensive’ way such as ArcView for Windows in order to view and query maps. Using the ‘traditional’ ArcView for Windows to view and query maps is still a rather expensive proposition. You not only need a souped-up PC (Pentium 166 MHz or higher, with 32 MB or more memory), but the license for ArcView which costs close to $1,000, connectivity to GIS database server which costs $100, ArcView training which costs $700, and the learning curve which takes about two weeks.
With AV-IMS in place, an end-user needs only a web browser (usually free nowadays) and the connection to the machine which serves as AV-IMS server. In a network environment, the connectivity is a given.
The AV-IMS Implementation at MCG. The DIST GIS Team obtained the AV-IMS licenses (The AV IMS extension for $500 and the AV-IMS deployment license for $10,000) from the GIS software vendor ESRI (Environmental Systems Research Institute) in May 1997. A Dell Pentium Pro 200 MHz PC running Windows NT operating system was procured earlier as the AV-IMS server. Naturally, the core ArcView for Windows software needs to be procured and installed also.
Phase I of the implementation (which concluded in March 1998) provided sample maps for the following departments:
(see map: upper left view is master page, upper right view shows Police Beats and Districts, lower left view shows Fire/Rescue Districts and fire station locations, and lower right view shows school locations and School Service Areas.)
With this Phase I implementation, any PC in the network (connected either through Token Ring topology or Ethernet) which has browser software installed can view the maps created for these departments and query the underlying information associated with these maps. For instance, if you are browsing the Election Districts map, you can query which council member represents a particular District. Similarly, if you are browsing the high school service area map, you can obtain the information such as school name, address, and phone number for a particular high school. Additional maps are being added to these departmental sub-pages. In addition, more sub-pages for additional departments will be added.
Enhancing the JAVA Applets. The JAVA applets bundled with AV-IMS only provides limited map browsing capabilities such as zoom and pan. In order to provide a higher degree of interactivity between the user and AV-IMS, steps have been taken--procuring JAVA Workshop and JAVA Studio and getting staff trained on JAVA scripting—to expand the functionality. Ultimately a user will be able to perform queries such as "I’m at 101 Monroe Street (or Monroe and Jefferson). Show me the bus route and schedule for going to Lake Forest Mall" or "My address is 101 Monroe Street. What’s the Election District and Precinct that I belong, which polling place do I go to vote, and what’s the shortest path for going there?"
Countywide Seamless Data Access via Spatial Database Engine
Traditionally the automation of large scale (such as 1" = 200’) base maps (planimetric, topographic, and cadastral) follows the map grids in a manual drafting environment. In the case of Montgomery County, the 660 map grids set up by WSSC was used to organize the various base map layers that were digitized. Arc/Info GIS software has a LIBRARIAN function to manage and provide access to these layers. However, due to the large amount of map grids in the library, query and accessing data in a countywide mode is very inefficient, if not impossible.
The GIS software vendor’s solution for this problem was SDE (Spatial Database Engine). SDE is a middleware that interacts between an industry-strength relational database management system (RDBMS) such as Oracle and the GIS software (Arc/Info or ArcView). With SDE, both the spatial data (coordinate strings) and attribute data (street names for street segments, fire incidents for fire-box areas, etc.) are stored in the RDBMS, allowing efficient storage and retrieval.
DIST GIS Team procured the SDE Server license ($20,000) and four client connections ($4,800) in FY 97 and has implemented the software application. So far, the property, roads, bridges, and contours layers have been uploaded into SDE. With these countywide seamless databases, we have supported applications for DEP and DPW&T (Facilities and Services Division, DFS). DEP maintains its water resources database by watersheds. DIST has developed an Arc/Info application for cookie-cutting the countywide SDE data layers into watersheds and saving it back as Arc/Info coverages. DFS routinely needs to identify candidate sites for facility planning purposes. A query on the countywide Property data layer to identify publicly owned land (see map) took less than 10 minutes (total elapsed time including display), whereas in a ‘traditional’ Arc/Info Librarian environment, this operation likely would take 5 – 6 times longer than with SDE.
Another application example that can take advantage of this countywide seamless database is for the Customer Counter at the Department of Permitting Services (DPS). Using an ArcView front-end, the user keys in street address or property ID and the system would display the subject property. Additional SDE data layers can be added to the display. Attributes such as acreage, zoning class, and permit processing status can also be made available.