The DEP Wetlands datalayer comprises two feature types, polygons and arcs (lines). The attribute codes in the polygon layer describe different types of wetland environments and the arc attributes describe line types based on adjacent polygon types or arcs defined as hydrologic connections.
The wetlands are interpreted from 1:12,000 scale, stereo color-infrared photography (CIR) by staff at UMASS Amherst. The interpretation is field checked by Department of Environmental Protection (DEP) Wetlands Conservancy Program (WCP). Completed interpretations are then scanned and converted into rectified polygons and lines using standard photogrametric techniques by a consultant under contract to the WCP. Final quality control is performed by WCP GIS staff. The polygons and arcs are merged into a single layer (in coverage format) and additional attributes are added for the polygon features. The arc features are coded based on the adjacent polygon types, and attributes are added to the annotation subclass wet. An overlay process using the 1:25,000 Hydrography layer codes the PALIS_ID and PWSID attributes.
The coding of the PALIS_ID and PWSID attributes was done using an overlay process and was not subject to the same quality control as the 1:25,000 Hydrography layer. Areas of wetlands in this layer may be shown as open water in the 1:25,000 Hydrography layer and so the coding of the PALIS_ID would not occur. Lines represented in the old 1:5,000 Streams layer are shown in this layer as hydrologic connections. These lines are only defined where they connect the various wetland types. These connections were not delineated within wetland areas, nor does they depict a complete stream network outside of wetland areas.
Because the source scale of the CIRs is 1:12,000, plotting of open water features at a larger scale when overlaid onto existing 1:5,000 imagery will reveal areas of open water that are not delineated as such. It should be noted that the resulting wetlands shown in this datalayer are for planning purposes only. Wetlands boundary determination for other purposes, such as the Wetlands Protection Act MA Act M.G.L. c. 131 or local by-laws, must use the relevant procedures and criteria.