What affects electrical resistance?

Answer 1

Primary Factors:
For a simple system like an electrical wire, there are three major things which will affect the electric resistance.
1. Resistance of wire conductor depends upon the material of which it is made.
2. Resistance of wire conductor is directly proportional to its length.
3. Resistance of a wire conductor is inversely proportional to its area of cross-section. (At least for low frequency voltage.)

Additional:
In general every material has a characteristic electrical conductivity (and resistivity) which determines how well it will conduct electricity. Metals have very high conductivities and insulators very low. The geometry of an object affects the resistance with the above-mentioned wire geometry being the most important example.

In general the type of material and the geometry are the primary factors in determining the resistance of an object, but there are other effects worth mentioning.

Temperature can change electrical properties of a material and there are some dramatic examples such as superconductors. Semiconductors can also have important temperature dependent properties. For most generic materials there is a rise in resistance with an increase in temperature but the effect is not usually large.

More exotic phenomena also exist, such as the change in resistance due to a magnetic field or nonlinear conductors which do not have a fixed resistance but rather have a resistance that depends on voltage. Conductivity through a gas is a dramatic example of the latter.

Answer 2

Temperature is the only factor which affects resistivity...

Apart from that the resisitivty will stay constant even if you change the dimensions of the sample of material