From: Sarah Hoffmann Date: Sat, 11 Aug 2018 12:47:36 +0000 (+0200) Subject: add FAQ from nominatim.org X-Git-Tag: v3.2.0~26 X-Git-Url: https://git.openstreetmap.org./nominatim.git/commitdiff_plain/569184a5b09a3bc348a774c0a387ca2e16299fbf add FAQ from nominatim.org --- diff --git a/docs/api/Faq.md b/docs/api/Faq.md new file mode 100644 index 00000000..cc6397d3 --- /dev/null +++ b/docs/api/Faq.md @@ -0,0 +1,43 @@ +# Frequently Asked Questions + +## API Results + +#### 1. The address of my search results contains far-away places that don't belong there. + +Nominatim computes the address from two sources in the OpenStreetMap data: +from administrative boundaries and from place nodes. Boundaries are the more +useful source. They precisely describe an area. So it is very clear for +Nominatim if a point belongs to an area of not. Place nodes are more complicated. +These are only points without any precise extend. So Nominatim has to take a +guess and assume that an address belongs to the closest place nose it can find. +In an ideal world, Nominatim would not need the place nodes but there are +many places on earth where there are not precise boundaries available for +all parts that make up an address. This is in particular true for the more +local address parts, like villages and suburbs. Therefore it is not possible +to completely dismiss place nodes. And sometimes they sneak in where they +don't belong. + +As a OpenStreetMap mapper, you can improve the situation in two ways: if you +see a place node for which already an administrative area exists, then you +should _link_ the two by adding the node with a 'label' role to the boundary +relation. If there is no administrative area, you can add the approximate +extend of the place and tag it place= as well. + +#### 2. When doing reverse search, the address details have parts that don't contain the point I was looking up. + +There is a common misconception how the reverse API call works in Nominatim. +Reverse does not give you the address of the point you asked for. Reverse +returns the closest object to the point you asked for and then returns the +address of that object. Now, if you are close to a border, then the closest +object may be across that border. When Nominatim then returns the address, +contains the county/state/country across the border. + +#### 3. I get different counties/states/countries when I change the zoom parameter in the reverse query. How is that possible? + +This is basically the same problem as in the previous answer. +The zoom level influences at which [search rank](https://wiki.openstreetmap.org/wiki/Nominatim/Development_overview#Country_to_street_level) Nominatim starts looking +for the closest object. So the closest house number maybe on one side of the +border while the closest street is on the other. As the address details contain +the address of the closest object found, you might sometimes get one result, +sometimes the other for the closest point. + diff --git a/docs/mkdocs.yml b/docs/mkdocs.yml index 4018433f..87d65363 100644 --- a/docs/mkdocs.yml +++ b/docs/mkdocs.yml @@ -11,6 +11,7 @@ pages: - 'Reverse': 'api/Reverse.md' - 'Address Lookup': 'api/Lookup.md' - 'Place Output Formats': 'api/Output.md' + - 'FAQ': 'api/Faq.md' - 'Administration Guide': - 'Basic Installation': 'admin/Installation.md' - 'Importing and Updating' : 'admin/Import-and-Update.md'