I imagine it'd be Central Kalos simply because:
1) It's Central Kalos. Note, Central. xD
2) According to the picture the white part seems to cover the Lumiose Gym.
But honestly I don't think it matters, since the Pokedex sub-titles are just a rough guide of where Pokemon can be obtained, and no wild Pokemon can be obtained in Lumiose. So yeah.
Hope I helped. :)