spelling vs orthography

spelling and orthography both are nouns.

Word	Noun	Adjective	Verb	Adverb
spelling	Yes	No	No	No
orthography	Yes	No	No	No

As nouns, orthography is a hypernym of spelling; that is, orthography is a word with a broader meaning than spelling:

spelling: forming words with letters according to the principles underlying accepted usage
orthography: a method of representing the sounds of a language by written or printed symbols

Other hypernyms of spelling include writing system.

spelling (noun)	orthography (noun)
forming words with letters according to the principles underlying accepted usage	a method of representing the sounds of a language by written or printed symbols