NO DATA is the home of MISSINGNO. It is a location in the Torren Region which can be accessed to battle MISSINGNO.
Two prerequisites are needed in order to reach NO DATA. First, the player must have upgraded the PikaTaxi to be able to Soar. Second, the player must have access to Gaea Town. Once reaching Gaea Town, talk to the blue haired man sitting on a bench who calls himself the Human Calculator. When asked to give him a calculation, tell him to divide any number by 0. The game will reach a runtime error and crash. After restarting the game, the player still be standing in front of the Human Calculator, and he say the answer is a random number. Next, talk to the EmolgaTaxi Guy to soar over Torren. Just south of Mist Island, a new area that looks to be a mess of textures, suspiciously labeled "Gaea Town", will appear on the map. Hover over to the middle of it to be forced to land. Walk north in the glitched out room to battle MISSINGNO. After the battle is finished, the player will be transported back in front of the Pokémon Center of the real Gaea Town.
Unlike the core series games, the area and events surrounding MISSINGNO are expected functionality and will not actually corrupt the game, even if it is caught.