Administrative Boundaries

admin_level=5 : District border till this level no conflict.

currently i used admin level 8 for city boundaries and 9 for suburbs (can see inside Colombo city).

admin_level=6 - Divisional Secretariat border
yes we can also use this one.

i left admin_level=7 because i am not clear about political seat concept. i don't have clear idea about this. are they overlapping with Divisional Secretariat border or not i am not sure.

in future if we realize we need to add this kind of intermediate border for safe side i left admin_level=7

if we clear about this we can use level 7 else we can keep for future

So that means city boundaries and suburbs not in province/district hierarchy. It's separate set consists with gramaniladari division
Okay then we can get level 7 for gramaniladari division.
So with level 7 we finish first hierarchy.
Then according to sadeepa's explanation we can start second hierarchy(which creates grouping gramaniladari divisions,consists one or more)
(municipal , urban , pradeshiyasaba)/ suburban (if exists)
So for second hierarchy we can use level 8,9 and 10

Which means if it municipal council,urban council or pradesiya Saba it will get level8
Suburbs will get level9

Still there is mess

How about Villages?

Then we will mix up 2 hierarchy .aren't we?
There will be no relation to level 6 to 7 it will jump to 9
Then new relation to 7 to 8 and again 9 to 7

It's it looks weird? ?

I think size doesn't matter.it's better to follow relation.

End of pradeshiya Saba tree we can add village in level 10

its seems to be we are now in good shape about sri lanka boundaries. after reading lot and finding more on osm indexing and addressing i think we can clear the last end of this mess .

here is my understanding about city/town/village and suburb

city , town, and village should have same admin level . because they don't have relation with each other. they are same admin units and populations is the only factor make it different.(i think that's why osm recommended to add population tag garmin map also categorize cities with population as i remember it has 5 or 6 mp codes for according to population)

suburbs will have +1 admin level to city or town , (city or town consists with suburbs) we may use +1 admin level for neighbourhood .

advantage of this classification is if split or filter with admin level 8 we can easily see all cities ,towns and villages.  this is great + for if we going to add addressing. In any kind of gps maps will work with this. (if we use 2 level program will look higher level first then lower since villages not inside city our addressing index will incorrect. its ideally match with suburb. usually addressing will mark as city/suburb or city -suburb   )


PS: after checking several maps i have some rough idea about why our city/town/village structure is not align with province/district system.
as my understand city/town/village admin system is form ancient Sri Lanka boundary system . which was ordered like this

රට/දිසාව/පත්තුව/කෝරලය/ගම

still in most of Survey Department maps we can see some these borders.latter villages with large population converted to towns administrative centrals turned in to cities. in current administrative system smallest unit is "grama niladaree vasama" it may or may not match with village.


so bottom line is  if it like this city,town and village will never going to align with new division system 

if we need to push GN division to after MC/UC/PC, yes we can. may be to level 10 . since after GN division there is no more smaller area we can use level 10 . i don't think we can merge towns/villages with GN division its totally different boundaries.

eg: for my area,my GN division is kamburugamuwa North. it contains part of kamburugamuwa , labeema and part of kotavila.kamburugamuwa west contain part of kamburugamuwa and thal aramba. so its clear that we cannot merge this two systems.

my idea is its no use of we wasting time on this minor boundaries. These boundaries use full for government and they already have good maps which supplied by survey department. its important to us mark towns and villages boundaries correctly because its only thing useful for us.


main usage of osm data is navigation. for navigation currently we are doing well on roads our next target should be searching places points or addresses. we dont have any support on this task form this kind of minor admin boundaries, only useful feature is cities towns and villages. no one in sri lanka write address as DC /GN . its always come as city/village. actually for address calculation purpose its very important to draw boundary of city/town or village.most of gps systems able to find aress using this bounds. (the same way how google give the places details )

if we are thinking to create good address system in our osm we need keep safe this city/village boundaries for good number of years. because of this situation i keep fist 7 levels for official boundaries and started 8 and 9  for town/suburbs(also most of countries use this level for city/town/village. in osm wiki )  i saw several times government maping project appear time to time and update one area and disappear again (like in gampaha area now). to avoid any mix with there mapping system its better to keep low values for city town villages.

any way i check most of boundaries in sri lanka map , i saw till level 7 is used (level 7 used in Batticaloa area previous mapping project done by DMC team. they may use same convention for gampaha also) .

if we use 7 for cities of towns we may conflict with DCM team.

@ last here is my suggestion

admin_level=1 : Not used
admin_level=2 : Country border
admin_level=3 : Not used
admin_level=4 : Provincial border
admin_level=5 : District border
admin_level=6 : Divisional Secretariat border
admin_level=7 : lets leave this for now
admin_level=8 :Municipalities and Township borders (Municipal council limits, Urban council limits, Major Town limits etc....)
admin_level=9 : suburbs(inside major city )
admin_level=10 : Grama Niladari area Minor settlements or not used