I'm waiting on delivery of my Navionics platinum card and have been reading up on relief shading overlay. My question is if I download data on one lake and then later download data on a second lake will I have both sets of data on my card or will the second relief shading data overwrite the first?

Thanks.....Richard

I think the answer to your question is it will overwrite the first. You chose the lakes you want to download by using an expandable box. You drag the borders to chose the area you want to download. My download area includes about 6 lakes in my area. You can change what lakes you want any time.
https://www.youtube.com/watch?v=ZHYzo6laVBU

That's what I think also. Got the card yesterday and will look at it today. I was disappointed that the lake I fish most often, Choke Canyon, is not included in the list for Relief Shading areas. Maybe Navionics will add this at some time but I guess I will use SonarChart Shading until then.