Another great site is Maptech historic maps the link is http://historical.maptech.com/
I use these maps all the time. The david rumsey map collection also has some great maps. that link is http://www.davidrumsey.com/
Hope these help.
The Sanborn digital map site has a key. It is found by clicking help, under FAQ click on features. There is an index and key.The link is http://sanborn.umi.com/HelpFiles/bwkey.pdf
hope this helps out. Sometimes it is a little difficult to read. Perhaps another member knows of a clearer copy...
I lived in essex and gloucester. The clammers are very watchful over their areas on the flats. You need a license to clam no matter what. I've run into that trouble before. The good thing is once they understand you're looking for bottles , they usually leave you alone. Also some of the local...