Do "landed" ships...

[Sathurn]

Do landed ships contribute noticeably to lag? And I do mean a lot of them like a user made city?

[sal_vager]

Only if you are within 2.5km of them, as they would be on rails and have no physics applied to them beyond that distance, so lading another craft there would be a pain.

You might also get some slowdown in the map as it has to render and track several craft in one spot, but other than that there should be no problems

[Karriz]

Only ships within 2,5 km are loaded, otherwise they're just showing up as a map marker that shouldn't cause lag.

[NannerManCan]

If your within 2.5 km of them then yes they do cause more lag. Dependiing on how many ships there are and how many parts they have will contribute to the amount of lag.