the desert
there is no specific place to find latias but after you battle the elite four latias or latios can appear randomly and you can keep track of its area through the pokedex
In ruby and sapphire
you will get it in sapphire. it can appear in wild grass if you are lucky.
Latias appears when you talk to the Copycat Girl and get her doll from the guy in the Pokemon Fan Club in Vermilion City. Upon exiting the building, Steven will tell you Latias is loose in Kanto.
Latias cannot be bred, which is the case for most legendary Pokemon.
You find Latias randomly in the wild on every route on the left side of the map. To make it easier to catch use repels. If youre pokemon are under level fifty latias will appear. If you didn't use your Masterball on Kyogre I recommend you use it on Latias.
latios and latias appear in random patches of grass and areas of water after you catch Rayquaza or make him faint.(after saving the world in Sootopolis.)
daa didnt you now tath?? easy you must talk to the guy in a museum and he gives you a rock . then latios and latias will appear!!
If you're still interested, I found the human form Latias at the end of chapter 310 and in 311.
I'm pretty sure that Latios is the only one of those two who appear in SoulSilver, if you want Latias you gotta trade with someone who caught it on HeartGold.
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In Pokemon Emrald Your Mom asks you a question. click on red.you only get it when you defeted the Pokemon league.when you are in the water surfing or in a patch of grass Latias might appear