the question i was answering was whether starports are necessary. they are.
proximity to harvestable resources is a historical driver of settlement beyond primary cities - first, often temporary and then more permanent as the workers desire to be close to their families and merchants desire to be close to settled populations that want to buy things. the wildcard in the BTU is agriculture - you're probably not going to have millions moving to the frontier for their 160 acre land grant and heavy industry exists so there is less impetus to spread out so much.
aspects of this is kind of what I was getting at.
to use a few examples of worlds colonized (typically around the star league era)
you will have a primary reason the planet was colonized
for example:
reasonable climate:
agriculture food, food animals or similar.
population relief
general expansion
semi nasty world, (similar to reasonable but with an issue, like occasional horrible storm seasons, lack of or contaminated water, dangerous and hostile flora or fauna, etc. ) :
in many ways similar to the reasonable climate reasons.
getting rid of shall we say medium security criminals.
removing unwanted ethnic groups, that can't get upgraded to more desirable worlds.
exploiting a rare or unique resource.
hell worlds: these are outposts or colonies established for ulterior motives.
scientific research
mining outpost/colony
emptying prisons of lifers/death row inmates.
military installation
manufacturing that involves horribly toxic/environmentally destructive processes.
or similar.
many times more than one "reason" may be combined.
expansion patterns:
these are going to be driven by a number of factors, a well equipped and funded settlement on a reasonably friendly world is likely to expand reasonably quickly and range from family dislikes neighbors, to grabbing a land claim etc. they will likely expand quickly and have lots of settlers showing up. this will lead to lots of Midwest style "towns" where there are a number of farms or similar anchored around a food storage facility and transportation hub. depending on factors, it may include a pad/runway/port for large transports or small dropships, whatever makes the most economic sense.
a more hostile world is going to expand more slowly and strategically because something like the small farm settlement or ranch is not likely to survive.
on a "hell world" expansion is going to be extremely slow and unlikely, in many cases it will be driven by offworld sponsors, rather than local population because its so difficult (or expensive)