At Woonona, residents on the western side of the Princes Highway see houses across the road where work is under way.

It's the same story for some residents along Gipps Street, North Wollongong. And residents on the Princes Highway at Towradgi are still waiting for the NBN, while about 100 metres up the road construction on the network is happening.

"You're always going to have that until we build out the whole country - there's always going to be that next module to build," NBN Co spokesman Darren Rudd said.

"There's always going to be someone across the street until we do the last module in 2020."

Modules are the coloured areas visible on the rollout map on the NBN Co website. These end down the middle of the Princes Highway or Gipps Street - or even a few metres up the road.

Each module encompasses about 2500 premises, which is why some appear bigger than others on the map.

When it comes to selecting the order of suburbs to be connected, things like the make-up of the population, the number of schools or the prevalence of commuters (who could telecommute through the NBN) don't matter.

Instead, Mr Rudd said NBN Co looked at a range of factors to decide where to build next.

"The Department of Communications did a comprehensive audit recently of serviceability of all those areas that are under-served and ranked them - we look at that," Mr Rudd said.

"We also look at where we've done work in the past, so we've spent a lot of time upgrading exchanges in Wollongong and Corrimal and Dapto.

"Where we have done work and have a workforce, and our delivery partners have a workforce, we start there."

The rollout in each area generally begins at an exchange and branches out from there. This why the rollout map shows several separate patches where work is under way, patches that slowly become larger as the rollout progresses.

The rollout map also shows what appear to be anomalies, such as very small pockets of Thirroul and Cordeaux Heights where the NBN is already available despite both locations being outside any module.

Also, within the Wollongong module, where work has begun, there is a block of land that already has the NBN. These are not errors but what NBN Co calls "greenfield sites".

They are sites where new homes or apartment blocks are being built and NBN Co gets the developers to include the NBN infrastructure during the construction.

The buildings are then given a temporary NBN connection, which is replaced by a permanent one when the rest of their area is connected.

"It's done because we don't want new apartments put in with old technology when we're rolling out the NBN and then have to go through and incur the cost, disruption and inconvenience of putting it in after they're built," Mr Rudd said.

When it comes to getting the NBN, Mr Rudd said it was just a matter of being patient because rolling it out across the country - and they aim for an even split between urban, regional and remote regions - was a big task.

"I've worked on these in Hong Kong, Taiwan, Japan," he said.

"When you've got places like Singapore, where you've got a lot of people in a very small geographical area, it's very easy to roll out a national broadband network.

"But when you've got a country the size of Australia and we've got to get to 8 million properties by 2020 and navigate the existing infrastructure, that's the challenge.

"It's a challenge of just getting the network rolled out everywhere. Everyone's going to get it, it's just going to take time."