The length and the material that the conductor is made from. Different wire sizes have different ohm/foot. The longer the length of the conductor the higher the ohms/foot.
Temperature also affects the resistance.
Silver has the least resistance, followed by Copper, then Gold, then Aluminum. Here are some published resistances in micro ohm-cm:
The material from which the conductor is made, the length of the conductor, the diameter of the conductor and the temperature of the conductor are all things that impact its resistance.
Yes, resistance is directly proportional to the length, and inversely proportional to the cross sectional area. R = p*l/A. Where R is the resistance of the piece of conducting material, p is Greek...