I tried nicolasdumoulin's approach
and it unfortunately left me with the same results that I had experienced earlier, missing segments of the administrative border. :[

Chriscf,
That's the map that I'm looking to make ! Unfortunately, I haven't figured out yet the correct rules to use for the Overpass API. :/

Through my searching, I found a couple suggestions in http://help.openstreetmap.org/questions/8273/how-do-i-extract-the-polygon-of-an-administrative-boundary

and I'll be testing those out in the next day or so to see if they will work.

Cool project !

I tried to run it and unfortunately received an error as follows:

BACKGROUND_COLOR = #000000
BORDER = 10
BREAK_DISTANCE = 0.8
COLOR_RANGE_STEPS = 128
CROP =
DEBUG = 0
GEOM_OVERRIDES =
GRID_COLOR =
IMAGE_SIZE = 2000
MAXSPEED = 0
MINMAX_DISABLING_NPOINTS =
MINMAX_ONLY =
MINSPEED = 0
OUTPUT = output.png
RUNNERS =
RUNNERS_OUTPUT =
RUNNER_COLOR = #FFFFFF00
RUNNER_DIAMETER = 5
RUNNER_TAIL_LENGTH = 1000
SRCDIR = /media/myharddrivesname/1archiveuntitled folder 2/
TRACK_COLOR = #FFFFFF78
TRACK_THICKNESS = 1

Use of uninitialized value in addition (+) at logdraw.pl line 143.
Use of uninitialized value in addition (+) at logdraw.pl line 143.
Use of uninitialized value in addition (+) at logdraw.pl line 144.
Use of uninitialized value in addition (+) at logdraw.pl line 144.
Use of uninitialized value in subtraction (-) at logdraw.pl line 146.
Use of uninitialized value in subtraction (-) at logdraw.pl line 146.
Use of uninitialized value in subtraction (-) at logdraw.pl line 147.
Use of uninitialized value in subtraction (-) at logdraw.pl line 147.
Illegal division by zero at logdraw.pl line 148.

The second osmosis filter that I run to remove ways information in the bounding box that I do not need:

osmosis --read-xml v5.02-extracted.osm --way-key-value keyValueList="highway.motorway_link,highway.motorway,highway.primary_link,highway.primary,highway.secondary,highway.secondary_link,highway.tertiary,highway.residential,highway.service,highway.unclassified,railway.rail,railway.light_rail,railway.tram,railway.subway,waterway.stream,waterway.river,waterway.riverbank,natural.water,natural.coastline,boundary.administrative" --used-node --write-xml v5.02-filtered.osm

Here's an update of how I progressed since then.

The problem:

When downloading data from OSM, the geographic area is (not always, but for the sake of this post, most of time) shaped in a rectangle defined by the bounding a north, east, south, and west coordinates (known as a bounding box).

When it comes to coastlines in OSM, the entire area is not downloaded, just the data within the bounding box. This can be a problem if your data partially contains a coastline and the data does not specify which side is land and which is water !

Thus, here's what you should do if you have a large coastline to render in osmarender.
(thanks to bobkare in the OSM IRC channel for the help).

1. download the tiles@home client.


2. Extract the t@h client, copy both ./close-areas.pl and the folder png2tileinfo to the folder that contains the .OSM file you wish to render.


3. Run ./close-areas.pl on the .OSM file
   As follows: ./close-areas.pl minlat minlon maxlat maxlon < theosmfile.osm > output.osm
   

After running close-areas.pl, my output .osm file, once rendered, still did not have water in it.
Why ?!
Through a couple trial and errors of running close-areas.pl, I also learned that the the bounding box order IS NOT the same as your minlat minlon maxlat maxlon . The bounding box order (used in the OSM API, [v.06]) is left,bottom,right,top sides of your bounding box;

but the parameters of the
minlat is the bottom (of your bounding box) (southern portion),
maxlat is the top/north;
minlon is the left/west;
maxlon is the right/east.

I had mistakenly entered the bounding box coordinates in the same order of the API, not the specific order used in close-areas.pl

The correct close-areas.pl was:./close-areas.pl 41.49503 -81.7291 41.51245 -81.69391 < input.osm &rt; output.osm

EDIT: I haven't fixed it yet I was able to render the coastline using an area of bounding box that consisted of the mall portion of downtown Cleveland (the above coordinates), for the sake of simplicity during this debugging process. However, when I attempt to run the above using the bounding box of the entire city of Cleveland (the same used for the Cleveland Neighborhood Map), the water is displayed everywhere on the rendered image, instead of just Lake Erie.