Special Resource Bonuses

[Destroyer]

Why do the special resources show with +1hammer or +1food in the trade negociation screen?

I have also noticed these bonuses in the city screen on the trade box.

These dont appear to affect anything though.

I have tried to see if there is any bonuses for a new city, but it does not look like it.

[nllsq]

http://apolyton.net/forums/showthread.php?s=&threadid=148162