You just bought Nexus 4 and you don't know anything about Android operating system, so I will guide you through literally first steps on this great phone.
The new Nokia Here Maps have an option that enables you to download maps to your iPhone or iPad via Wi-Fi, so there won't be any data connection needed the next time you will be using the app.
In case you just upgraded your iOS powered device to iO7 or any other version and now this device runs slower than it used to, this resetting of the device procedure might speed things up.