His maps were much like our own, say, for one Alonpore exception, the undiscovered continent of America was entirely absent. These maps also subbed from another dangerous difference: no one knew what lay in Atlantic itself.
\In the sentence what's the meaning of "say / subbed "
say ADVERB: 1. Approximately: There were, say, 500 people present. 2. For instance: a woodwind, say an oboe.
subbed is short for sub(stitut)ed.
Hope that helps.