Issue link: https://read.dmtmag.com/i/43993
Recreational trail datasets often lack in availability, accessibility and sometimes credibility, so Trails Co-op uses several different sources to create a centralized database of recreational trails with the up-to-date trail names and information, such as location, length, com- ments and additional information. "The most important tool for me is the trail profile," says Gretchen Volker Smith, Environmental Resource Specialist, U.S. Army Corps of Engineers. "I've designed rides around this key information, often- times missing from most trail-ride books." Building the Database The Trails Co-op is based, for the most part, on Google APIs, including Maps and Earth, and the spatially enabled, open-source MySQL database platform. The trails data have been compiled through several years from federal geodata clearinghouses, municipal data sources, FTP sites and formal data requests mainly from the USFS, NPS and BLM. Many of the acquired datasets came in differing schemas and formats that took extensive work to compile into one database with the same schema. One of the main steps for trails integration was to assign and correctly match names to trails. Many federal datasets came in the form of Shapefiles, Geodatabases and ArcINFO coverage files that included lookup tables, which were used to derive and assign trail names. But some trails came with little associ- ated information, so additional data requests were made or names were assigned based on partial name or after landmarks using topographic or forest visitor maps. After names were assigned, all datasets were placed into the same schema of data types, field names and attributes. A text-based minimum-bounding rectangle, which includes the minimum and maximum latitude and longitude for each trail, was created as well as additional attributes to give Google Earth an area to zoom when users click on a trail. After all trails were in an acceptable attribute format, all the datasets were re-projected to the WGS 1984 datum to match the coordinate system used by Google Earth. The ArcGIS field calculator was used to populate the minimum/maximum latitude (Y) and longitude (X) for each trail, along with the approximate mileage. Because trail data from different sources vary greatly in quality, detailed trail lines were generalized to assist with easier handling. If all lines were high resolution and greatly detailed, it would lower the speed of draw- ing and database handling. To generalize the linework, a maximum allowable offset of 0.015 (change from input to output) was selected as a balance between resolution and file size. After trails data were standardized, feature classes from the personal geodatabase were exported to MySQL query format with a program written using ArcObjects-Visual Basic for Applications for ArcGIS. From there, the queries were loaded into the MySQL database on the Web server, which converted the geometry data to "well-known binary" for optimized storage and handling, all while maintaining the appro- priate attribution. Each trail also was given a unique ID to allow for easier indexing and querying. The functionality of Trails Co-op can be split into client- and server-side functions. Functions that required interaction with the database fell on the server side and were coded with VBscript ASP, while func- tions that didn't require interaction with the database fell on the client side and were coded with JavaScript. Server-side functions include those built to handle data passed to them as parameters, such as querying the database and returning the appropriate code and data, inputting data into the database, and extracting lFigure 1. The Trails Co-op Google Earth interface shows the lower 48 U.S. states. SEPTEMBER 2O11 / WWW . GEOPLA CE .C O M 27