I have never been to Louisville, Kentucky, but even if I had I’m sure all of my business or exploration there would have been above ground. But beneath parts of the city of more than 600,000 is the Louisville Mega Cavern, an underground space of 100 acres created by years of mining rock. 

The cavern is so big it has more square footage than the 94-story One World Trade Center. The space is so massive you can take a two-hour ziplining adventure into parts of the cavern most people never see. You can ride a tram that takes you on a geologic adventure to explore some of the 17 miles of underground corridors. A small portion of the mega cavern contains a display of 80 life-sized mechanical dinosaurs. During the holidays, the Lights Under Louisville show is a drive-through light show of more than 40 displays with more than 900 lit characters and more than 6.5 million points of light. 

So, imagine having to survey this massive area and account not only for horizontal boundaries, but vertical boundaries and every rock column left by more than 40 years of mining stone to keep the cavern from collapsing. That task fell to Qk4, Inc. Ben Shinabery, vice president for land survey at Qk4, led a team that took 10 months and more than 700 man hours to complete the survey. 

Shinabery writes about the unique challenges that such a large survey presented, especially since most of the work needed to be done underground. It’s an interesting story starting on page 12. 

Also in this issue, xyHt contributor Marc Delgado takes a look at some innovative geospatial applications that are being used to create digital twins of European city roadways to solve the problem of traffic congestion in major metropolitan areas. In another story, Juan Plaza looks at the new National Geodetic Survey’s forthcoming datum changes. 

I hope you enjoy the issue. 
-Jeff Thoreson