[OSM-talk] Tagging schema

Andrew Errington a.errington at lancaster.ac.uk
Mon Oct 5 09:51:07 BST 2009

On Mon, October 5, 2009 15:36, Lester Caine wrote:
> ( Egil - a little aside, while a check box for boolean would be nice,
> there is still an element of 'NULL' - that is in addition to setting a
> boolean tag, one still needs to decide if it should or should not be
> present )

Checkboxes these days /can/ represent three states.  There are usually two
states: checked (or ticked) and not checked (an empty white box).  In most
GUIs it is possible to represent a third state, perhaps a grey square
filling the box.  (This is different from the control being disabled,
usually shown by being greyed-out).  The meaning of this third state
depends on the application, but it can mean NULL, unknown, conflicting
source data, or whatever you want it to mean when it's not True or False.

I'm not sure that this third state is particularly useful or intuitive,
but I know it means something different to True or False when I see it.

I like the Japanese style of conveying information like this.  A cross
('X', often red) means 'no', 'none', 'wrong', 'false', or 'not'.  A circle
('O', often green) means 'yes', 'correct', 'available', 'OK', or 'true'. 
A triangle (hmm, can't do that in ASCII) means 'maybe', 'limited',
'restricted', 'perhaps'.  Obviously their meanings depend on context, but
they are well-known in Japan (and not too confusing outside of Japan).

In fact, here's a handy-dandy reference:


(The use of 'playstation' is incidental to the article).


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