WordNet (r) 3.0 (2006):

sparsity
    n 1: the property of being scanty or scattered; lacking
         denseness [syn: sparseness, spareness, sparsity,
         thinness]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "sparsity":
   chinchiness, chintziness, dearth, exiguity, fewness, infrequence,
   infrequency, meagerness, miserliness, niggardliness,
   occasionalness, paucity, poverty, rareness, rarity, restrictedness,
   scant sufficiency, scantiness, scarceness, scarcity, scrimpiness,
   seldomness, skimpiness, slowness, smallness, sparseness,
   stinginess, stringency, thinness, tightness, uncommonness,
   unfrequentness, uniqueness, unusualness