This is a difficult question to answer because any answer will be heavily dependent on one's definition of bias. To attempt to answer, I'll be working off of the Merriam-Webster definition of gerrymandering:
to divide (a territorial unit) into election districts to give one
political party an electoral majority in a large number of districts
while concentrating the voting strength of the opposition in as few
districts as possible
I believe that Norwegian system of reapportionment avoids both prongs of this definition of gerrymandering. Wikipedia outlines the Norwegian process:
Out of the 169 seats in the Storting, 150 are apportioned among the 19
Counties of Norway with deliberate bias in favor of rural areas. The
number of seats for a county is decided using a formula in which a
county receives 1 point for every inhabitant and 1.8 points for every
square kilometer of land area. However, the bias is reduced by the 19
compensation seats, which are given to parties that are
underrepresented. Thus the system does not have a great effect on the
partisan composition of the Storting, but does result in more MPs
coming from rural counties. Electoral researcher Bernt Aardal
calculated that if the 2009 parliamentary election had been conducted
without this bias, the Labour Party and Progress Party would both have
lost a seat, while the Red Party and Liberal Party would each have
gained one, reducing the majority of the Red-Green Coalition from 3
seats to 1.
Does the Norwegian system divide election districts to give one political party an electoral majority?
- According to a well-credentialed political scientist, removing geographic weights in the system would have been inconsequential in its outcome. Check out his research (which highlight several other, perhaps even more proportionately designed, electoral systems) (Aardal, B. (2011). The Norwegian Electoral System and its Political Consequences. World Political Science, 7(1), pp. -. Retrieved 30 Jun. 2017)
- The proportionate design of the Norwegian system gives less prominent party organizations more power than the US system does.
- The geographic districts remain largely the same over time
Does the Norwegian system concentrate the voting strength of the opposition (in this case, we'll assume that's the minority party(s)) in as few districts as possible?
- Since the geographic weights are counterbalanced with compensation seats, no geography would be disproportionately favored (as outlined in the Aardal study).
- The majority party cannot punish the minority party by changing or modifying district geographies once in power
In conclusion, I believe that the Norwegian system avoids both 1 and 2, uses a mathematical formula, and therefore satisfies the requirements of this question.
I'm also sure that several other countries have similar systems and I'm sure the study I've linked provides further insight into how they work/operate.