There is nothing unique with the SD card on a 2013 assuming you are using TomTom. Get yourself a standard SD card of at least 8gb, but important to have a high speed one (Small circle on the front with a number like 8 or 10) higher the better.
I guess the card in your slot is the original Mazda one as supplied and has probably expired; it was a limited capacity card and as updates were added over the years the card quickly became too small. It is likely the previous owner copied the files some time ago and subsequently added them to his own card which he/she kept on the transfer of the vehicle, leaving you with the old card and outdated set-up.
If you are registered with TomTom Home and don't mind "investing" in new maps you should be able to copy from their web site via your log-in; get your debit/credit card out and then you can download. If not registered, download TomTom Home and use your e-mail address as your log-in. Once you have paid your money & downloaded the file via "TomTom Home" you have ownership, so if the files don't transfer first time to your card you can play around until it finally works. If something goes wrong TomTom will help after all you would have paid your money. You can add Live Traffic later and update for the rest of the year.
In essence, be prepared to pay for at least one year of updated maps as you won't get much help otherwise from TomTom, and you may as well add the traffic - at extra cost - it is extremely useful and I have recouped the cost several times over.
One small thing however, there is a "loop file" which is added to your card from the car's own software in the nav device and it doesn't copy very well on your pc files; so pop the card in the slot on the car before you start. Might not actually seem to do anything at first as there will little else on the card. Then do your paid for download, you may find you have added your maps and it still doesn't work very well once in the car slot. If so take the card out from the car slot and put the maps on again, there is a lot of disparity on the "loop file" which I suspect is down to TomTom trying to frustrate you even further. It does suggest in the adding/updating process once you finish that you should do it all again and logic will probably make you question it, but is it not successful first time that might be why. Important ensure the slot door is closed when the card is in place in the dash.
If you go live traffic, when you try it for the first time might be 15 minutes before it appears and try to be in a good Vodafone area. If all else fails phone Tomtom cust service from your car with your account log-in details and if you are live through the nav system they can look at most things for you. It has been suggested the files cannot be copied, don't believe a word of it!
Finally feel smug that you didn't go through all the issues with TomTom and the Live Traffic throughout 2012 and 2013. Took a year to get matters sorted and nobody would take ownership. Ask XTrail man, He'll remember.
Alex.
