With exception of selected U.S. waters and applicable updates, other "VDU Patches" published on this Web Site are made available for DoD customers who have authorized access to baseline DNCs. The VDU Patches support updating of the worldwide DNC, which consists of 29 Geographic Regions.

NGA's VPF Database Update (VDU) software was designed to meet digital correction and update requirements of VPF data products resident at remote user sites. The U.S. Navy and NGA believe that "commercial patch" technology has matured significantly in the past several years, to the point where it is now a viable solution to VDU requirements. Although there is a need for future rapid update of all VPF data, the immediate need for this capability is to support the Digital Nautical Chart (DNC) program. DNC update requirements are unique due to the frequency, volume and criticality of update information to support safe electronic navigation.

Commercial patching technology uses "differencing" software to compare an updated DNC dataset with the baseline (original) DNC dataset. A small patch file containing differences between DNC chart files that have been modified since issuance of the baseline edition is redistributed via CD-ROM or by electronic means (Internet). Shipboard navigation systems are then able to use patch-apply software to update DNC files from certified NGA-produced patches. The goal is to have continual up-to-date information available for electronic download to support "Hands Off" at sea updating.