Using this improvement effectively is hard, but possible with good planning. The improvement acts as an adjacency bonus to nearby tiles; however, the tile itself cannot be worked by a Citizen! This means that rarely should you build two Nazca Lines next to each other. The only exception to this is when you have a large desert city which has expanded to the fourth tile ring and beyond, you can put Nazca Lines on the tiles belonging to the fourth ring and farther, since they improve the yields of other workable tiles and do not cost you anything. Also, look for those great expanses of flat Desert (the Nazca Line can only be built on a flat tile) which have resources on them, then build a couple of Nazca Lines around the resources. This will enhance the resource tiles' yields at the cost of the other tiles being unworkable; however, most Desert tiles have no yields anyway so you won't lose anything.
Nazca Lines are even better in mixed terrain, where flat Desert tiles are mixed with other terrains (Plains, Grassland), or with Rivers with Floodplains. Even water tiles benefit from Nazca Lines, so you could get Faith generation from the sea!
If you have a desert city with a lot of Hills and you plan to build Petra in it, you should not use this improvement in combination, as the yields from Petra are so much more substantial than yields from the Nazca Line. This improvement should only be used when you have a city settled in sub-optimal desert areas with low Food yield and you tried to rush for Petra but failed, as this improvement can work as a backup plan to keep that city going. Don't go and settle new desert cities just because you are the Suzerain of Nazca when Petra is already built elsewhere, as Nazca Lines are not strong or impactful enough to create a bustling desert city for you.
With favorable terrain and some planning, the Mapuche civilization can use Nazca Lines to boost the Appeal of their Chemamull improvements, in turn providing higher Culture. Districts for Australia can also get a yield boost for each adjacent Nazca Line, and Alcázars and Seaside Resorts will enjoy a boost in Science and Gold yields respectively.
The Nazca lines are huge geoglyphs—figures cut into the earth, created by the Nazca culture that lived in Peru between 500 BCE and 500 CE. Some figures may be older, from the Paracas culture, since the figures follow some of the design motifs found in Paracas textiles. The designs are fragile despite their size, and are made by removing a thin layer of red pebble topsoil to reveal the lighter rock underneath. The Nazca lines are stylized depictions of birds, animals, and human figures. Some of the Nazca lines are simple marks oriented with various celestial landmarks.
The Nazca lines might have been associated with invocations of favorable rainfall from sky deities, but our understanding of Nazca culture is not complete enough to provide anything besides plausible explanations. A variety of less plausible explanations for the lines have been offered, many of which fail tests of parsimony, if not strain credibility to the breaking point.
Changes to the arid desert environment of the Nazca plateau and their popularity as tourist attractions are the biggest threats to the preservation of the Nazca lines. If rainfall patterns change, the lines may literally wash away. If careless tourists continue to damage them, they may disappear beneath the footprints of their admirers.