A gazetteer is a geographical dictionary or directory, providing information about places, their locations, and sometimes their populations, features, etc.
However, you could consider "non-geographical dictionary" or "non-topographical reference work" as a kind of "opposite" in terms of subject matter.
For example, if you're looking for a reference book that is *not* focused on geography, you could use a dictionary of synonyms, a dictionary of quotations, or a dictionary of scientific terms.
It's important to note that "antonym" is typically used for words with opposite meanings, and a gazetteer doesn't have a word with a directly opposing meaning.