Part 1: Just started — no badges

Just started — no badges opens 5 areas.

Where to go

1. Route 101

   Wild: Zigzagoon 95% · Lv 2, Poochyena 5% · Lv 2, Chikorita Lv 5, Chimchar Lv 5 +10 more

2. Petalburg Woods

   Wild: Wurmple 60% · Lv 3, Zigzagoon 35% · Lv 3, Shroomish 5% · Lv 3

3. Route 102

   Wild: Zigzagoon 60% · Lv 2, Lotad 35% · Lv 2, Seedot 35% · Lv 2, Ralts 5% · Lv 2

4. Route 103

   Wild: Zigzagoon 60% · Lv 2, Poochyena 35% · Lv 2, Wingull 5% · Lv 2

5. Route 104

   Wild: Zigzagoon 95% · Lv 2, Taillow 5% · Lv 3, Wingull 5% · Lv 2

Everything you can have caught by this checkpoint · Open the interactive guide

It also doesn't say when 9 of its areas open up, so they are listed together in the last part rather than guessed into the story.