Why was longitude and latitude so hard to find in the 18th century?

Answer 1

There were very few people who owned GPS receivers at that time, even rich people,

noted scientists, and top navigators. Moreover, those who did received no signals, as

the GPS satellites had not yet been launched.

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Latitude could be found in the 18th century by using the sun, moon and stars. It wasn't until chronometers (clocks) became accurate and reliable, that the longitude of a sailing ship's position could be found.

Note: GPS receivers are a modern device, and had nothing to do with the 18th century!