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.
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.
The layer's point attribute table contains the following items:
|SFTYPE||Surface feature type|
|NUMBER||Unique point ID|
|SPOT||Elevation in meters|
|OQ-ID||Source orthophoto tile number|