5.1 TOWN OF AMHERST 5.2 TOWN OF BOYLSTON, MA
5.1. Town of Amherst
In November 1998, the town of Amherst started working on Photogrammetry and GIS Base Mapping project. The implementation of this project was subcontracted to engineering company Merrick & Company, Aurora, Colorado. The first stage of the project includes production of the color aerial photography of the town at the scale 1"=400' to meet the requirements of 1"=40' scale horizontal accuracy (± 1.0') and 2' contour vertical accuracy (± 1.0'). Also, for an outlying watershed area 1"=800' scale will be used to meet 1"=100' horizontal accuracy (±2.5') and 5' contour vertical accuracy (± 2.5') requirements. To perform the photo control, the advanced GPS technology will be used. The approach will take advantage of the existing 75 survey control points. After Airborne GPS and Fully Analytical Triangulation, a photo type Digital Terrain Model, Planimetric, Topographic and Ortho Image databases will be created. The resulting orthophotos scale will be 1"=100' with 0.5' pixel size. The next step will be creation of the parcel coverage. For this purpose the "best fit" parcel automation technology will be used. First, the existing Assessor tax maps will be registered to the digital orthophotography. Then, the parcels will be digitized using the landbase as the controlling source. In this approach, the technician will use ground evidence to register the property boundaries. Fence lines, hedge rows, building outlines, ditch lines, lakes, and streams would be utilized to help determine parcel boundaries. The technician will make an adjustment of the block of parcels to the ground evidence (landbase) and then digitize them.The following features will be converted:
· Street Rights-of-Way
· Railroad Rights-of-Way
· Easements (if shown)
· Subdivision Boundaries
· Hydrology - (Creek, Stream or River lines along parcel boundaries)
· Parcel Boundaries
· Lot lines
· Parcel Centroids
· Town Boundary Lines
The following items will be included as text annotation:
· Town Limit Designation
· Parcel Number (PIN)
· Water Body Text
· Power Line Text
· Street, Road, Highway Name
· Legal Dimensions (Lot Dimensions and Deed Area Text)
· CAMA Linkage Number
Source: Merrick & Company reportIn 1998 the town of Boylston as a part of Master Plan update had its parcel maps converted to the digital form. It was done by the Central Massachusetts Regional Planning Commission (CMRPC). The first part of the process was georeferencing of the paper maps. Control points were derived from orthophotos. Anywhere from four to ten control points were used for each map. Usually points that were very easily identifiable on both maps (analog and orthophotos) were used. For example, road intersections, political boundaries, power lines, etc. However, orthophotos covered only three fourths of the town. So, in the areas where orthophotos were not available GPS coordinates were taken and these points were utilized for georeferencing purposes. Anywhere from nine to twelve points were taken for each map sheet.
When the georeferencing procedure was completed, maps were digitized using the software Carta Linx produced by Clark Labs in Worcester. The creation of the digital parcel layer consisted of the two steps. First, roads were digitized from orthophotos, which were used as a background image. Second, parcel lines were digitized from paper map sheets, and manually coordinated in their placement. In those cases where it was possible, parcel lines were digitized from orthophotos. For the portion of town not covered by orthophotos a different method of conversion was used. These maps were scanned by MassGIS Executive Office of Environmental Affairs in Boston and then vectorized. After that, these maps were imported into Carta Linx and incorporated into the greater coverage.
After digitizing was completed, the following attribute fields were created using ESRI ArcInfo software:
1. Area (created by ArcInfo)
2. Perimeter (created by ArcInfo)
3. Map identification number (created by ArcInfo)
4. Map number
5. Block number
6. Lot number
7. Combined map-block-lot field
8. Count (created by ArcInfo)
9. Field containing the Boylston Assessor's Landuse Data as represented in the 1993 Assessors Land Use Codebook
10. Chapter 61 field - depicts Chapter 61 (Agriculture), Chapter 61A (Forest), and Chapter 61B (Recreation Use Areas)
11. Field indicating errors on the parcel sheet (f.e. parcels without block numbers or duplicate numbers on the same sheet)
12. Landuse code
13. Field showing parcels used for recreational purposes including water-based recreation, spectator recreation, and participation recreational areas.
14. Acreage of the parcel.
Source: Menard, Stephen. Central Massachusetts Regional Planning Committee.
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