Resize to scale multiple layers at once in Illustrator

I have approx 20 layers in illustrator (a world map with layers for capital city names, small city names, rivers, oceans, etc). I want to increase the size of this map, so I need to increase the size of every layer without distortion. I have tried to Select all - group - transform, but all layers disappear off the artboard and are bigger than the dimensions I typed into W x H boxes. Any advice appreciated. Thanks!