[Geocoding] How Nominatim works and where are seas?

[Sarah Hoffmann]

Hi,

On Tue, Jul 07, 2015 at 11:48:13PM +0200, Štefan Kiss wrote:
>   My name is Stefan and I am from Slovakia. I am a blind user of computer and for the work with PC I am using a screenreader which cann me to read a text from screen. I cann work with text, e-mail, webpages, sound but not with pictures and maps. But I am interested in geography and I would like to find some possibility for reading maps.
>   I found a Nominatim service and I thought that it is a chance for me. I am living in Slovakia (48 lat and 18 lon) and I sent to Nominatim a sequence of queries where lat was 48 and lon was step by step decremented from 18 to 0. It was great for me to know what about countryes are under my Slovakia. I think - this is a way for blinds - how they cann read a maps and to create some image about the world. 
>   But now I hawe 2 questions to you. 
> 
> 1. On the webpage of Nominatim service is written:
> 
> "...The following examples use Nominatim to reverse geocode. This is the process where you begin with a geographic coordinate and the nearest known address is returned."
> 
>   Please, what it means? When I send to Nominatim a coordinates 40 18 
> (http://nominatim.openstreetmap.org/reverse?format=xml&lat=40&lon=18&zoom=18)
> and I get result Apulia, Italia, means it that I am really in Italia or the result is only the nearest known address and my location 40 18 dont must be in Italia?

Yes, that is how the reverse call in nominatim works. It looks for the
closest house or point of interest to the coordinates you have given
and returns the address of the object. If there is no house or POI
in a reasonable distance, it falls back to looking for the closest
street, then the closest town and so on.

If you are not actually interested in a specific address but, say,
only the town or region you are in, you can use the zoom parameter
to control at which level Nominatim starts with the search for the
nearest object. For example, zoom=17 will start searching for the
nearest street, zoom=9 starts with counties. This should allow you
to get the granularity you need.

> 2. When I sent to Nominatim a sequence of queries and I went from 48 18 down to 10 18, I saw, that the seas are missed. I know that under Europe is Adriatic sea but in Nominatim results I go from Italia to Admas Tisal and Libia. (Admas and Tisal are tagget with tag address29 without other tags about Country or city).

Geographic features like oceans or the Adriatic seas are not
included as an area in the OpenStreetMap data, so Nominatim
doesn't have that data and will simply return the information
about the closest land mass.

Sarah