Usually billboards are OK. As for why MadVapes chose that location, it would be wise to find out why. Perhaps you can do some stealth research and ask an employee next time you visit.
As for the ordinance, check out MuniCode for your area. That will tell you if there are any ordinances that are keeping vape shops out of that area. It also may be the landlords there. If they aren't friendly to vaping then it doesn't matter what the ordinances say.
Download our "how to pick a brick and mortar location" if you have not already. It has some other tools to determine why they picked the location they did. Perhaps the demographics in that area (i.e. population, income, etc...) did not jive with their business model. This means that if you can create a brand that appeals the demographic, and find a vape friendly landlord, you could open a shop there.
Hope this helps.