As discussed elsewhere, we need to be careful with the building of Nether portals due the crazy things they can do.
Also we used to have some carefully constructed portals which allowed for fast travel between things, but with the destruction of the old nether they have all gone.
However the real world portals are still there, and some of them were wrecking havoc with the portals in the nether, I kept coming out in other peoples basements etc.
As for simplicity while getting the town hall and togservation deck portals on line, deactivated a number in the spawn village (the ones I came out of instead of the town hall portal.
I then went and moved the town hall portal in the nether to the correct altitude so it should only ever link back to town hall (unless another portal is in close proximity with Town hall.)
I have also built a portal to the togservation deck and to my basement and they are all link with very nice walkways (otherwise you would have to fly as they are in the middle of the air)
WARNING - The section below contains maths that may cause some headaches for those who don't like maths, feel free to skip to below
I have some tips for portal building, remember that the nether is smaller than the real world (well not really but it is for portals) so you need to divide the real world x and z postion of your portal by 8 to get its postion in the nether, ie the Togservation deck is at x=-200 z=57 so in the nether its at x=-25 z=7
(have to round due to minecraft not doing fractions)
However when it comes to height, (altitude, or y) its the same as the real world.
This is where you run into problems ie with my portal (y=6) and the togservation deck, (y=122) they are really close together in the nether, ie about 4 blocks or something in the x and z but when it connects back to the real world it multiples the x and z by 8 and leaves the y and then looks for the closes portal.
Which is uses basic trig (think back to high school maths), thus if my portal in the nether is at say 80 it will connect to the togservation deck because it works out closer, however it its at say 32 (where it is now) it goes to the portal in my basement.
WARNING END- No more maths.
So to keep things simple I suggest keeping most portals at the same heights as it removes the having to do any real maths other than the divide/multiple by 8 which we can all do with the help of a calculator
So I propose that all real world portals within the spawn village be built below y=30 (with exception of those that can't ie togservation deck etc) and all portals in the nether which link to them be built on the same level as mine which is just above the lava.
This will hopefully prevent incorrect linking to portals.
However if you wish to build a one way portal from the real world to the nether than you want it to link to another portal which won't return you to the same portal, if thats the case you need to get the maths right or ask someone to help.
Sorry for the epic post, but I think we need to discuss this before we all go and build heaps of portals