The first step is identifying the 26 locations. The second is to take the IATA airport codes for each location (note "It's At These Address" in the flavortext; also note that the IATA code for "Mamai" in Papua New Guinea is MAP). They are:
1 PHL PHILADELPHIA, Penn. 2 STA STAUNING, Denmark 3 WMC WINNEMUCCA, Nevada 4 DLE DOLE, France 5 KQA AKUTAN, Alaska 6 IEJ IEJIMA, Japan 7 BWI BALTIMORE, Maryland 8 MVB FRANCEVILLE MVENGUE, Gabon 9 XZA ZABRE, Burkina Faso 10 NAE NATITINGOU, Benin 11 ERF ERFURT, Germany 12 CUN CANCUN, Mexico 13 TPJ TAPLEJUNG, Nepal 14 HBO HUMBOLDT, Nebraska 15 VJB XAI XAI, Mozambique 16 OSI OSIJEK, Croatia 17 QXE SORA, Italy 18 FDR FREDERICK, Oklahoma 19 GFO BARTICA, Guyana 20 RIF RICHFIELD, Utah 21 ZGI G-DS RIVER, Canada 22 JNU JUNEAU, Alaska 23 UCE EUNICE, Louisiana 24 AOL PASO DE LOS LIBRES, Argentina 25 LYT LADY ELLIOT ISLAND, Australia 26 YKS YAKUTSK, Russia
The first and second letters of the airport codes use each letter of the alphabet once, giving a substitution code used to decrypt three M answers.
Ciphertext: ABCDEFGHIJKLMNOPQRSTUVWXYZ Plaintext: OWULRDFBENQYVASHXITPCJMZKG
Reading down the third letters gives the message "LACEAJIBAEFNJOBIEROFIUELTS." Decrypting this with the above code spells "Your one-word answer is DECRYPT."