OVERVIEW

These data layers are used to index the 2008 USGS Color Ortho Imagery tiles and the DVD schemes used for their distribution. They are stored in ArcSDE as follows:

• COQ2008INDEX_POLY - 2008 USGS Color Ortho Index (for GeoTIFF and MrSID 1,500m x 1,500m tiles)
  
• COQ2008MOSAICS15CM_POLY - 2008 USGS Color Ortho MrSID 15cm Mosaics Index
  
• COQ2008MOSAICS30CM_POLY - 2008 USGS Color Ortho MrSID 30cm Mosaics Index
  

See the PDF Index for more detail and as a reference when ordering or downloading the imagery.

The 1,500m x 1,500m tiles index polygons were created by using the Generate Fishnet command in ArcGIS 9.2 and converting the line layer to a polygon feature class. The origin of the fishnet was chosen such that the maximum amount of 2008 imagery was covered after projection from the UTM Zone 19N coordinate system to NAD83 Mass. State Plane Mainland Meters. Each polygon is 1,500m by 1,500 meters, insuring that the original 15cm and 30cm resolutions would be preserved in the projected imagery and be fully contained in each tile. The TILENAME attribute was populated by creating centroid points for each polygon, adding its XY state plane coordinate to the point (with the Add XY tool). A new attribute was added to the point layer comprising the first 4 digits of each X and Y coordinate. A spatial join transferred the 8-digit string to TILENAME in the polygon layer. Each polygon was then coded for resolution and which mosaic would include it, for each resolution. The Dissolve tool was used to create the MrSID indexes, using the MOSAIC15CM and MOSAIC30CM attributes.

The polygon attribute tables contains the following items:

Attribute	Description	Contained in Feature Class(es)
TILENAME	Unique 8-digit ID for each 1,500m x 1,500m tile	COQ2008INDEX_POLY
RESOLUT	Available resolution for the 1,500m x 1,500m tile:      - 15cm and 30cm  - 30cm Only	COQ2008INDEX_POLY
MOSAIC15CM	Name of MrSID mosaic comprising 15cm tiles	COQ2008INDEX_POLY COQ2008MOSAICS15CM_POLY
MOSAIC30CM	Name of MrSID mosaic comprising 30cm tiles	COQ2008INDEX_POLY COQ2008MOSAICS30CM_POLY

These datalayers are maintained by MassGIS.

Last Updated 3/5/2009
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