Criteria for constructing the catalogs: (for more details see: Bianchi et al. 2014, J. ASR 53, 900; Bianchi, L. et al. 2011, MNRAS, 411, 2770)
1) only observations with both FOV and NUV detectors turned on are included. This is useful for any science analysis where the fraction of sources with a given FUV-NUV color is of interest, or to estimate the fraction of sources with significant detection in both FUV and NUV over the total number of NUV detections. Note that the basic GALEX database gives FUV magnitude = -999 in both cases when the FUV detector was off, or the FUV detector was on but the source's FUV flux is below detection threshold.
More observations exist in the GALEX archive taken with one detector off (mostly FUV); those can be found in the galex.stsci.edu MAST database.

2) only sources within 0.5 degree of the field center are included, to avoid sources with poor photometry/astrometry near the edge, and rim artifacts. This makes the catalogs useful for statistical analysis of sources with homogeneous quality, without great loss of area coverage (also considering that overlap exist among several fields). Users interested in a particular source that happens to fall on the rim of a GALEX filed, should obtain its measurements from the main database and carefully examine the quality.

3) we retained sources with NUV magnitude errors less or equal 0.5mag (see Figure 4 of Bianchi et al. 2011 MNRAS , and Figures 2--4 of Bianchi et al. 2011 ApSS for effects of error cuts on the resulting sample statistics).

4) The general GALEX database contains all measurements for sources with repeated observations. We removed duplicate measurements to produce a unique source catalog as follows. GALEX sources within 2.5'' of each other, but from different observations, were considered duplicates. In such cases the object from the observation with the longest NUV exposure time was retained, and - in cases of equal exposure times - the object closest to the center of the field of view.

See also these review articles for useful information on GALEX data: Bianchi, L. 2009, 320, 11, DOI: 10.1007/s10509-008-9761-3 ; Bianchi, L. 2011 ApSS, 335, 51; DOI: 10.1007/s10509-011-0612-2 ) )

Reference: Bianchi, L., Conti, A., and Shiao, B. 2014, J. Adv. Space Res. Vol. 53 (2014), 900; DOI: 10.1016/j.asr.2013.07.045 ; astro-ph 1312.3281
The ultraviolet sky: An overview from the GALEX surveys. link to ASR article (open access, i.e. free) or download manuscript pdf or go to astro-ph 1312.3281

Get the catalogs :

CATALOGS of UV sources( " BCScat" AIS and MIS )
==> download the catalogs HERE in csv files, or fits files: for AIS, get GUVcat instead!
==> from MAST casjobs BCScat_AIS superseded by GUVcat_AIS, BCScat_MIS still available
==> from Vizier (see GUVcat )