isopleth
noun
iso·pleth ˈī-sə-ˌpleth 
1
: an isoline on a graph showing the occurrence or frequency of a phenomenon as a function of two variables
2
: a line on a map connecting points at which a given variable has a specified constant value
isoplethic
ˌī-sə-ˈple-thik
adjective 
Word History
Etymology
International Scientific Vocabulary is- + Greek plēthos quantity; akin to Greek plēthein to be full — more at full
First Known Use
1908, in the meaning defined at sense 1
- on the qui vive
- on the quiet
- on the rack
- on the ragged edge
- on the razor's edge
- on the rebound
- on the receiving end
- on the record
- on the right side of
- on the right side of (an age)
- on the right side of an age
- on the right side of someone
- on the right side of the law
- on the right track
- on the right/wrong side of (someone)
- on the right/wrong track
- on the rise
- on the road
- on the road to recovery
- on the rocks
- on the ropes
- on the run
- on the same page
- on the sauce
- on the scene