Is the following more aptly described as a simile or an analogy?

"to be able to procure its own entertainments, and to subsist upon its own stock, is not the prerogative of every mind. there are, indeed, understandings so fertile and comprehensive, that they can always feed reflection with new supplies, and suffer nothing from the preclusion of adventitious amusements; as some cities have within their own walls enclosed ground enough to feed their inhabitants in a siege. but others live only from day to day, and must be constantly enabled, by foreign supplies, to keep out the encroachments of languor and stupidity."
—samuel johnson