Wisconsin constitution
Article IV: legislative
Section 5

The senators shall be elected by single districts
of convenient contiguous territory, at the same time and in
the same manner as members of the assembly are required to be
chosen; and no assembly district shall be divided in the formation
of a senate district. The senate districts shall be numbered
in the regular series, and the senators shall be chosen alternately
from the odd and even−numbered districts for the term of 4
years.

Structure Wisconsin constitution