I believe there is a code written into the game that gives the civ you are playing a greater chance of starting on a lattitude that roughly corresponds to the historical start of your civ. Of course there are other factors that also affect your starting location. The resource location is mostly random, but obviously oil is place near desert, rubber near jungle, etc.
At least for me, either consciously or unconsciously, I like to start on land that looks like the land I think my civ would have started out on anyway so there is a tendancy to re-roll until you get something that looks good. Example: desert and flood plains if egypt, forests and hills for germany or the celts.
So, if you are always starting near hills as the celts (a more northern lattitude), you have a good chance of getting iron nearby. Spain, would also be more likely to draw a more southern location and this would reduce the chance of iron due to the inherrant terrain of a southerly lattitude.