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Hello. You CAN use author to mean the person who originated the item in question. It is usually better, however, to use a word that relates to the item. For example - the author of a piece of music is a composer. The author of a painting is a painter, or another piece of artwork - an artist.
I think the best word for engravings and paintings is artist.
For a map I'm not certain. Technically it would be a cartographer, but you may not always use that word unless it is in a technical context.
Author is usually used for a piece of writing, whether it's a novel, a poem, or even a newspaper article, although you could also say novelist, poet and reporter respectively.
I hope that helps
