I have base map on the HDS7 and can only zoom to 50 ft. I have Insight maps on the HDS8 and can zoom to 20 ft. I have yet to get an answer about this. I questioned this phenomenon on Lowrance facebook. I believe billblb had zoom problems with the Navionics south chip, but when he switched to the Insight, zoom was fine. I may have misunderstood billblob though.