As a disclaimer, please note that I am not a lawyer. As such, this should not be accepted as legitimate legal advice; always consult a lawyer, when it comes to legal issues that concern you.
You might be covered by "Fair Use"
In general, you might be covered by "Fair Use". You are using the derived maps for your own personal use, and you are not profiting off them; nor are you misrepresenting the original authors or owners, in any way.
As long as you ensure private, personal use; you should be fine. That said, I am assuming you have legal rights to the game, to begin with; it is certainly not legal if said game was illegally acquired for this purpose.
There are always exceptions
That being said, your location of residence does make a difference. Some locations have laws that differ to others, and depending on the circumstances, your legal requirements may differ.
In most cases, you can also be sued for anything. Assuming the company acting as the "claimant" wishes to pursue legal action, you still have to go to court to prove that you have a legitimate claim to use the files in that way. In many cases, you could be in trouble with the sheer legal fees involved in having such claims thrown out.
As such, the best advice is always to consult a lawyer. If the cost of said consultation out weights the cost of finding an alternate solution, find an alternate solution. Consider that a lawyer might advise you to find an alternate solution, anyway, due to the sheer fickle nature of copyright law.
This is very unlikely to become a criminal case
I feel that I should make a final point, in regards to another answer. It is very unlikely that your actions could be considered criminal; even then, doing so would be a long stretch. Assuming legal action, at worst, you would be required to pay damages to a party.
Assuming legal action, assuming you comply with said legal action; this is not an issue that would lead to a jail sentence; at least, not of its own merit.