You did not mention PASDA, Pennsylvania Spatial Data access, http://www.pasda.psu.edu/
The most recent series of photos are orthorectified at 0.5' per pixel and cover a 10,000' x 10,000' grid. At least photos from 3 different recent years are available from the statewide aerial map as well as conservation photos USGS maps and lidar topographic data also on a 10,000' x 10,000' grid. I typically download the most recent orthophoto and the Lidar contour shape file. I start by bringing in the contour file into a blank CAD drawing and it shows up on the proper SPC location. From the ends of the contour lines I create a 10,000 x 10,000 grid box. The orthophotos come in at size 1 and need to be referenced to the coordinates in the TFW file which is in the zipped folder and scaled, 10,000 for an engineering scale drawing and different for an architectural scale drawing. The orthophotos and contour files are labeled by the SPC Easting and Northing values of the upper left corner, however the insert and scaling point is the lower left corner. Some orthophotos are available in 5,000' by 5,000' sized files. For my survey projects I have joined up to 4 sets of photos and topo files in one CAD drawing. My software allows me to clip the visible area of the photos to encompass my project and I also trim the contour lines to that clipped grid.
Paul in PA
