Your question is extremely broad. In general, building codes are designed to help us build more sustainable, livable, prosperous communities. King County, WA, which is where Seattle is located, has done an outstanding job over the last 20 years with a master growth management plan.
Most of the core areas of the different cities in the Seattle metropolitan area have made huge strides in making these cities more walkable, closer to the mass transit that is being built and refined. It takes a certain amount of density for buses and light rail to be viable.
The way building codes work for developers and builders, is that it gives them a set of rules to follow so we don't just end up with an urban sprawl mess. Most of the towns around Seattle are creating "urban villages" with restaurants and shops within walking distance. You can still find the rural life style in areas of King county.
For access to information on the different cities in the area, you can go to my website, http://www.karenmcknight.com and click on About the Area.
I am happy to answer more specific questions if you have some. I have worked with builders and developers my entire career and have sold the Seattle area for over 20 amazing years.