How many letters does the top answer for “a graphic representation of numerical relations” have?

The most common answer is nomogram (8 letters).

Crossword clue: a graphic representation of numerical relations

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

nomogram 8 letters wn-def

a graphic representation of numerical relations

nomograph 9 letters wn-def

a graphic representation of numerical relations