MassGIS Data: Digital Elevation Points from 1990's Aerial Imagery

April 2003

The points in this layer were created using Digital Terrain Model (DTM) data points collected during the production of the 1:5000 Black and White Aerial images.

Overview

The points in this layer were created using Digital Terrain Model (DTM) data points collected during the production of the 1990's Aerial Images . These points are accurate to National Map Accuracy Standards (+- 1.5 meters). In ArcSDE the layer is named ELEVATIONS_PT. MassGIS distributes the data in Shapefile format each shapefile is named P<OQ_ID>, where OQ_ID is the SHEET_ID from the Orthophoto Index layer.

Production

The points were produced using the ARC/INFO GENERATE command. The INPUT file was a .GEN file produced with an awk script which contained DTM point coordinates. The items NUMBER and SPOT were added to the .PAT using JOINITEM; their values were obtained from a .DAT file produced with the same awk script. Finally the item SFTYPE was set to 1 for mass. All of these data were extracted from the original DTM files collected on stereo analytic plotters. The points are tiled with the Orthophoto Index Grid coverage, which was used as a CLIP coverage as the DTM points overlap 5-10 percent in both directions.

Attributes

The layer's point attribute table contains the following items:

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SFTYPE	Surface feature type
NUMBER	Unique point ID
SPOT	Elevation in meters
OQ-ID	Source orthophoto tile number

Maintenance

This datalayer is maintained by MassGIS. For related datalayers see:

• Elevation Contours (1:5,000)
• Topographic Breaklines
• Digital Terrain Models (DTMs)
• Digital Elevation Model (1:5,000)
• Shaded Relief (1:5,000)