If all the ice on earth would melt, the effect on the shape of the continents wouldn't be too extreme. Coastal areas would be flooded, but only in few places the water would come significantly distances inland.

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Problem is that the majority of all people does live in these coastal areas. Not sure about the numbers, but a rough guess would be one third to two third of all people on Earth having to move inland. While Japan still looks like Japan, I think the number of people who would have to move would be over 90% and they already are awfully short in building space. And with Northeast China, Thailand, Bangladesh, and the American East Coast Gone, it's plain to see that a lot of people would be directly affected by wet feet. And that doesn't even yet mention South America and Africa, where I'm not so familiar with population distribution, but the numbers are probably very significant as well.

With less ice, less sunlight would be reflected and instead be absorbed by the land and the water, which might increase temperatures quite significantly. More sunlight and more ocean means more evaporation, which means more clouds. Which in turn means less sunlight that reaches the oceans. And then we are back at the problem of climate being one of the most complicated systems in the universe known to men, and predicting any weather paterns would be difficult.
There would be new areas that don't get any rain at all anymore, but overall I would expect a lot of storms with massive amounts of rainfall., for which none of the places that are not drowned yet would be prepared. Would easily take a hundred years or more for people to figure out how to make a living in that world. At which point the number of people might be drastically lower depending on how sudden the change is. If it is gradually over 500 and you would assume the process started about now on Earth, it might not even be a great problem as post-industrial countries always seem to shrink at significant rates and the worlds population might very well be down to 3 billion or less by that time and people have a lot more technology that would help easing the transition of constantly moving entire cities every couple of dozen years.
If compressed into about 100 years, it'd be the end of the world as we know it.