Mapping

by Kurt Buermann
Fall 2004

A Sharon Friends of Conservation watchword is “promote.” We hope to promote a better, wider appreciation of Sharon’s conservation lands by leading hikes. Another way we are supporting this goal is mapping Sharon’s hiking trails. A map of the King Philip’s Rock and Perkins Conservation Land is presently available.

This spring Jim Barron and Kurt Buermann dusted off the GPS tracker and began an exploration of the Massapoag Trail. A preliminary map is now available with a finished version due in another month.

The procedure is to walk the trails wearing a hat with a small Global Positioning System (GPS) unit attached to the top. Strange as it appears, height insures the GPS satellite signals (from multiple satellites) are not inadvertently blocked by the body as a low satellite would be if held in the hands or pocket. If you think of the GPS signals as beams of sunlight, you can see how an object on top of your head would be illuminated while a low sun behind you would throw a shadow on an object held in lower in the hands. It is also important to map in the spring or fall when foliage is at a minimum. The GPS signals are very weak and can be blocked by dense leafy overhead.

Stage two is to download the GPS tracks onto a topographic map program. This provides a picture of the tracks on an actual map background of woods, wetlands, hills and dales.

At this point a transparency of the tracks can be made for projection and tracing on to a more detailed map than provided with the basic Topo program.

SFOC has been very fortunate in having the assistance of April Forsman of the Town’s Engineering Department provide some high quality maps using the Massachusetts GIS (Geographic Information System). In general these maps are more detailed than those available on the retail market.

There is, at the end, a process of hand drawing. For example, where GPS mapper has veered off the trail to investigate a false lead and returned, a confusing side spike will show. This can be edited out with a computer program. Another curious phenomenon is to see the GPS track offset from known landmarks—say the end of a street. This is because many maps were made before GPS, with its uncanny accuracy of down to 20 feet, came into use. Here again, hand corrections must be made.

In addition to mapping, SFOC members have renewed original faded trail markings as well as done some trail grooming, particularly as concerns greenbriar growing across paths. Trash is also removed as we go along. Where needed we supply guiding signs.