GEOLOGIC DATA INTEGRATION IN THE NATIONAL GEOLOGIC MAP DATABASE

The National Geologic Map Database (NGMDB) "phase three" prototype is a combined effort of the AASG and USGS to harmonize data sets from differing sources and serve them in a format that can be consumed by web browsers or web services. It builds substantially on the project's 10-year effort to develop standards for a common data structure and controlled science terminology for geologic map and science data.

This NGMDB prototype integrates data from Arizona, the Pacific Northwest (Oregon, Washington, and Idaho), as well as several national data sets, at scales of up to 1:100K. Requests for more detailed data are passed on to the state surveys.

The prototype is facilitated by a custom-programmed data import tool that allows the user to match data in fields from an input database source, such as state geologic compilations, to the database schema used as a backend for our web map service. Fields in the input table are matched to corresponding fields in the NGMDB schema. Subsequently, unique values from each input field are matched to corresponding terms in controlled vocabularies defined by the NGMDB.

On the server side we employ Mapserver and PostGIS, two components of an Open Source GIS service stack. Mapserver is configured via mapfiles to display and symbolize map data from shapefiles for quick response to map drawing requests. PostGIS is used to answer queries by the user and to enable interaction with the database so that registered experts can update the database through a GeoWiki.

The capacity to read and write GeoSciML will allow integration from many sources. Once the data import tool is used to create a fully converted data set, it is exported to GeoSciML. This file can then be published on any website for harvesting by other GSML-aware services. We subsequently import this file into the full NGMDB data structure and optimize it for rapid web delivery by building generalized (less vertices) versions of shapefiles for use in Mapserver, as well as full resolution versions for display when a user is zoomed in to a sufficient level of detail. All data are also available as web services (OWS) provided by Mapserver.