Where to open your shop so the most shops fit in every room. Shops can't open too close to an up or down arrow, or too close to another shop. Packing them edge to edge from one end, instead of anywhere, fits more on every floor.
Floors, ladders and arrows come from the game's own map data (maplestory.io, MapleStory Classic World). The spacing rule isn't published, so it's measured from real shops in stream frames and screenshots: the closest two shops we've seen were about 115 apart, and the closest shop to an arrow about 65 away. The top floor in a busy room really does hold the 8 shops shown here. If the game tells you "you can't open a shop here" on a spot, nudge the sliders and tell the guild.