I don't see the need to create sub-categories either, but it will be great to have different options.
Using different markers inside the same category will be a plus specifically for categories such as: Restaurants, Accomodations, etc.
In this way, the user will notice the difference between a chinese restaurant and a italian restaurant.
Also, we can set up a check mark close to the search tab, to search only in the hotspots showing in the map. In that way, if we are seeing the category: Restaurant, and we search for italian, only the italian restaurants will be visible. Right now, if we type the word italian, anything containing the word italian will be visible.
Talking about the search tab, it could be nice to add some logical parameters to the seach tab like 'AND' and 'OR'. Right now we can only search for 1 specific word, or phrase. Implementing this, we can get rid of the check mark close to the search tab, considering that we will be able to search: "italian and restaurant and pizza" if we are looking for an italian restaurant selling pizza.