How can I increase the density of residential zones?

I've been playing the newly release SimCity 2013 for about a day but I'm really struggling with increasing my population with completely covering almost every inch of the map.

While income is not a problem I cannot seem to increase the happiness of my residents enough to encourage upgrading to a higher density. I have the proper roads in place, i.e. a medium density street to support medium density. However, all residence just stay as low density. Adding parks, sportplex, services (fire, police, health), results in an increase in land value and the residence simply upgrade to a higher wealth residence (i.e. mansion) and the population remains low.

What is the key to encouraging density growth, i.e. to get my low density residence to upgrade to apartments, without causing land value to sky rocket?

Land value and happiness are separate concepts.

• Land value aka desirability encourage wealthier sims to move in.
• Happiness encourages density increases.

Residential happiness comes from shopping! Turn on the commercial dataview and make sure that shoppers can go from residential zones to commercial zones with available goods. (Goods resupply automatically at 6 am and 6 pm. Goods have nothing to do with freight).

Residentials without money or without nearby goods will instead go to parks to get happiness. This happiness is just as effective at growing density as shopping (ie. your buildings will grow). However, there are some downsides. Parks cost you money, while commercial buildings pay tax. Parks take up more space to get the equivalent capacity of commercial buildings. Parks also increase land value - so you may accidentally bring in wealthier Sims than you really want (wealthy buildings hold fewer people).

If you need more jobs, you might need denser industrial zones. Industrial happiness comes from making shipments of freight. Turn on the industrial view. If there is a large pile of shipments at any building, that industrial is in trouble. Make more commercial zones or trade buildings to receive those shipments. Once received, those shipments will automatically vanish at some point allowing more to be received.