The co-ordinates above are not for the cache, but for suggested parking for this and Cipher Progression #1.
The Caesar Shift held firm for centuries, but eventually Islamic scholars found a weakness. In their studies of the Qur'an, they had noticed that some letters of the alphabet occurred more often than others; a fact which holds true for any written language.
This means that using a technique called frequency analysis, someone could decipher the message without needing the key. To obviate this, Leon Batista Alberti (1404-72) proposed alternating two keys, which would half the frequency distributions and make the cipher harder to crack.
This idea was then extended in the Gronsfeld cipher, which could use a key of any length, further smothering the frequency distributions.
You can check your answers for this puzzle on Geochecker.com.