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Overview
The Digital Orthophoto Index layer is a 4,000 by 4,000 meter grid in MA State Plane coordinates which serves as an index for the digital orthophotos, scanned USGS Quad images, and some vector data layers.
The MA State Plane projection splits the State into Mainland and Island Zones, and the orthophoto images as produced are referenced to the correct Zone. Thus, two orthophoto grid templates exist for the Commonwealth. This represents a change from other MassGIS datalayers which are registered to the Mainland Zone only. The Island Zone contains Martha's Vineyard, Nantucket and the Elizabeth Islands. The Mainland Zone layer is stored as OQMAIN_POLY and the Island Zone is stored as OQISLE_POLY.
The naming convention for each grid cell is based on the NAD83 meters coordinate pair for the lower right corner of the cell. The Grid ID is composed of the first 3 digits of each coordinate in this xy pair. For example, a grid cell with xy coordinates of 253000m 942000m at the lower right corner would have an ID of 253942. All datalayers registered to these index covers will have the grid number ID as part of their name.
Production
The index grids were generated by the ARC/INFO GENERATE command. The PROJECT command was used to orient the grids to the MA State Plane meters coordinate system and the two zones. Each grid cell is 4000 meters by 4000 meters.
Attributes
The OQx polygon attribute table contains the following items for each grid cell:
| SHEET-ID | 6 | 6 | I | Unique 5- or 6-digit OQ tile ID based on the first 3 digits of the lower right corner XY coordinate pair in Mass. State Plane NAD83 Meters |
| PROJECT | 3 | 3 | C | Name or project under which orthos were flown |
| DATEPHOTO | 8 | 8 | I | Date of orthophotography |
| DATEDIGITA | 8 | 8 | I | Date orthophoto received from vendor |
| DATECONTOU | 8 | 8 | I | Date 1:5,000 Contours entered into OQ library |
| DATECONTRO | 8 | 8 | I | Date control was completed |
| DATEPOINTS | 8 | 8 | I | Date 1:5,000 Elevation points entered into OQE library |
| DATEROADS | 8 | 8 | I | Date 1:5,000 Road Centerlines entered into library |
| DATEWET | 8 | 8 | I | Date 1:5,000 Wetlands entered into OQ library |
| DATESTRM | 8 | 8 | I | Date 1:5,000 Streams entered into OQ library |
| USGSPHOTO | 8 | 8 | I | Date of USGS-produced 1:12,000 orthophotos (0 if image not available) |
| PROJ_AREA | 8 | 8 | I | Vendor's project area, indicated on CD label |
| CD-ID | 8 | 8 | I | Vendor's CD ID, indicated on CD label |
| CD_COPIES | 8 | 8 | I | Number of CD copies received from vendor |
| COMMENT | 20 | 20 | C | |
| INDEX-ID | 4 | 5 | B | Tile ID in the OQ and OQE libraries' Index coverage (used for shapefile naming) |
| COQMOSAIC | 5 | 5 | C | Name of half-meter MrSID mosaic for 2001 Color Ortho Imagery |
| COQMOSCD | 10 | 10 | C | Name of CD containing half-meter MrSID mosaic for 2001 Color Ortho Imagery |
| SDE_MOS | 1 | 1 | I | Name of ArcSDE image mosaic in which tile is included |
| SDE_MOS2 | 1 | 1 | I | Name of ArcSDE image mosaic in which tile is included for overlap |
| YEARPHOTO | 4 | 4 | I | Year of black and white 1:5,000 orthophotography |
| CD_CODE | 17 | 17 | C | Concatenation of PROJ_AREA and CD-ID |
Maintenance
This datalayer is maintained by MassGIS. The DATEWET and DATESTRM items in the OQMAIN_POLY attribute table are updated by DEP GIS Group as new (which are developed by OQ tile) become available.
For more details see the Orthophoto Quads Index Map .
In late 2002 and 2003 several tiles were added to the layer to account for color orthoimagery tiles that were not obtained for black and white imagery. The SDE_MOS and SDE_MOS2 items were added to the OQMAIN_POLY attribute table in January, 2004.
Three tiles were added to OQMAIN_POLY in February, 2005, to cover Noman's Land (island south of Martha's Vineyard). Three others were added in March, 2005, to account for the extent of future ortho imagery.