The map will map out the location of your IP address and is usually right on.
Here is what is happening. The cable company will assign you an IP address, but that address will not be public until you go through their router onto the internet. That router could be located far away from your home location and in such a situation, the address will reflect the location of that router, not your home PC.
I am just curious, how many miles was it off by? Correction - I should say how many miles away is their router from your home
Best regards,
Jim.