Two and a half years ago, the software engineers behind Google Earth, the searchable online replica of the planet, were poised to fill an enormous data gap, adding the two-thirds of the globe that is covered by water in reality and was blue, and blank, online.

But until then all of the existing features on Google Earth  mountains, valleys, cities, plains, ice sheets  were built through programming from an elevation of zero up.

“We had this arbitrary distinction that if it was below sea level it didn’t count,” recalled John Hanke, the Internet entrepreneur who co-created the progenitor of Google Earth, called Keyhole, and moved to Google when the company bought his company in 2004.

That oversight had to be fixed before the months and months of new programming and data collection could culminate in the creation of simulated oceans. On Monday, the ocean images will undergo the most significant of several upgrades to Google Earth, with the new version downloadable free at earth.google.com, according to the company.