We complete construction of a catalog containing improved astrometry and new optical/infrared photometry for the vast majority of NLTT stars lying in the overlap of regions covered by POSS I and by the second incremental 2MASS release , approximately 44 % of the sky .
The epoch 2000 positions are typically accurate to 130 mas , the proper motions to 5.5 { mas } { yr } ^ { -1 } , and the V - J colors to 0.25 mag .
Relative proper motions of binary components are meaured to 3 { mas } { yr } ^ { -1 } .
The false identification rate is \sim 1 \% for 11 \lesssim V \lesssim 18 and substantially less at brighter magnitudes .
These improvements permit the construction of a reduced proper motion diagram that , for the first time , allows one to classify NLTT stars into main-sequence ( MS ) stars , subdwarfs ( SDs ) , and white dwarfs ( WDs ) .
We in turn use this diagram to analyze the properties of both our catalog and the NLTT catalog on which it is based .
In sharp contrast to popular belief , we find that NLTT incompleteness in the plane is almost completely concentrated in MS stars , and that SDs and WDs are detected almost uniformly over the sky \delta > -33 ^ { \circ } .
Our catalog will therefore provide a powerful tool to probe these populations statistically , as well as to reliably identify individual SDs and WDs .