analog layouts deals with matching ...... the main contraints are the area and mtching.
In digital layouts the main constraints are the clock signals data signal and control signal routing to reduce the skew problems.Area and matchins are not a constraint
When you do some signal analog layout, the matching and shielding should be considered, and when you do some power analog layout, the safe of the device should be considered.
By the way many tools can help you do some digital layout but analog layout design is a art which more depend on the designer's experience.
the very goal of a analog design decribes the difference between them.
in digital design,we need faster switching .so sacrifice the power.
but in analog we need the both.
faster operation and high power at high frequencies.
thats why analog design is more difficult than digital.
analog layout ASIC (Application Specific Integrated Circuit) which mean the design is done manually and not automatically like FPGA in digital design if u want more information u can read the book name Advanced Analog VLSI Circuit Design. Phillips