Building the Salem Witchcraft GIS

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Digitizing the Upham Map

H. Researching Locational Data

Two initial methods were used to locate these features on our base data, obtained from Massachusetts GIS: address matching, and searching the GNIS database.

Address Matching

The process of address geocoding, or address matching, involves comparing a precise postal address (123 Main Street) with a database of streets that contains address ranges for that street (100-199 Main Street). GIS software products take the known address, compare it to the attribute data for street layers, and interpolates a point on the line approximating its location. In this example, the address of 123 Main street would be placed closer to the beginning of the street with a range of 100-199, rather than to the end. An address of 149 would be placed almost exactly in a the middle.

Furthermore, the Census Bureau's TIGER database is not known for it's positional accuracy. The Bureau claims an accuracy of only +/- 167 feet.

Thus address matching is not an exact process, but it provides us with a starting point for further work in locating a building. After identifying these preliminary locations, we then overlaid the data with aerial photographs to find the exact control points for the Upham Map.

The following table shows the sites and addresses that were matched:

**Existing Sites Depicted on Upham Map**
address	city	zip	name	Upham no
149 Pine	Danvers	01923	Rebecca Nurse House	95
171 Holten	Danvers	01923	Sarah Holten House	93
4 Elerton	Danvers	01923	Daniel Rea House	48
199 Hobart	Danvers	01923	Nathaniel Ingersoll's Ordinary	148
238 Conant	Danvers	01923	Bridget Bishop (Edward Bishop)House	68
67 Centre	Danvers	01923	Parsonage	149
Essex & North	Salem	01970	Jonathan Corwin House	151
Essex & Washington	Salem	01970	Meetinghouse of the first church of Salem	160
Forest & Hobart	Danvers	01923	Salem Village Meetinghouse (1692)	173
Hale & Dane	Beverly	01915	John Hale House	107
Hanson & South	Salem	01970	Gallow's Hill	172
Hobart & Centre	Danvers	01923	First Church	174
Rt 1 & Rt 62	Danvers	01923	Joseph Putnam House	39

The address matching process resulted in this point coverage:

GNIS Matching

The GNIS system provides access to coordinates of 2 million cultural and physical features in the United States. It is not a perfect resource and, as with address matching, it provides only the starting point to locating more precise data through aerial photographs.

Users can search the GNIS database by the name of the feature, and limit the search by geographic location. Thus we could search for "Cedar Lake" and limit returns only to those features named "Cedar Lake" that are located within Essex County, Massachusetts. The search returns include geographic coordinates that can be converted to points in the GIS system.

After comparing Upham's Map with contemporary maps from the US Geological Survey, we identified these features that appeared on both sources:

**Contemporary Features Identified on Upham's Map**
contemporary feature	feature	Upham site	county	latitude	longitude
Danvers State Hospital	hospital	Hathorne's Hill	Essex	42.58111	-70.975
Humphreys Island	island	Island in Humphrey's Pond	Essex	42.52139	-71.00278
Wills Hill	summit	Wills Hill	Essex	42.59667	-71.02417
Cedar Pond	lake	Cedar Pond	Essex	42.51944	-70.98611
Wenham Lake	lake	The Pond or Great Pond	Essex	42.59306	-70.89306
Whipple Hill	summit	Thorndike or Whipple Hill	Essex	42.57083	-70.95833

There are four ponds in the area known as "Cedar Pond." Thus the returns from the search resulted in 9 points, including three worthless (to us) "Cedar Ponds." These were discarded.

The following image represents all matched points. Here, the point represented by the yellow cross indicates the "Cedar Pond" listed above.

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Salem Witchcraft Papers | March 1692 Animated | The Putnam Family

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