[OSGeo Africa] Is a map a measuring product ?

[Hanlie Pretorius]

Hi Peter,

As a disclaimer, I haven't read the bill(s) to which you refer.

Sounds llike another case of wanting to run before we can walk. What's
the point of these bills if the actual facilities (national measuring
standards, SABS) are falling apart?

When I started thinking about this, I realised that it's actually
quite a philsophical question.

What I understand by the term 'measuring product' is this: If I
measure the temparture of a bowl of water, I use a thermometer
(instrument) and the 'product' is the reading in degrees. I can give
that reading to a client but I have no control over how the client
uses it. The client could write it down, but transpose the figures. So
my measuring product is still correct, but its use has corrputed it.

A surveyor can measure a site for a client and produce a printed map
of the site. In this case, the map is a measuring product. The client
can use a ruler to measure a distance on the map and incorrectly apply
a scale conversion and end up with an incorrect map product. This
could be a 'secondary' measuring product I guess. If the secondary map
product is used somewhere and it causes damage of some kind, the map
maker should be able to repeat the client's action and come up with
the correct answer to prove in that way that the primary measuring
product was correct.

But virtually all maps do have errors. I can see this leading at worst
to people not wanting to share their data for fear of being jailed
because of the errors in their data. And at best I can see maps full
of disclaimers about the validity of the data.

I can think of cases in which the map is the secondary measuring
product and any measurements taken off it would be tertiary measuring
products. If I just assemble other people's data into a map, I didn't
do the measuring, someone else did. This could perhaps have the
positive effect that people would be more vigilant about the pedigree
of the data that they use.

Metrology and measuring standards use the concept of 'traceability'.
Measuring instruments (and therefore their products) should be
traceable to a national and then an international standard to ensure
that 5 degrees C in Pofadder means the same as 5 degrees C in Alice
Springs.

Would this be possible for the instuments that surveyors use to create
maps? Can you 'calibrate' a total station? And what if the problem
lies in the network of control points, rather than your instrument?

I'm not a surveyor, so I can't really answer these questions. Suppose
I use a GPS to find the coordinates along a hiking path that I can't
see on aerial images or for which I don't have erial images. I can
publish that path on a map and, strictly speaking, it's a measuring
product. But I don't really have any way of checking it, of making it
'traceable'. I can at best check it from a few control points if I'm
lucky.

If I give this map to a friend with the caveat that the data has some
uncertainty in it, should I really be facing jail for publishing this
hiking route? I think that's crazy.

Perhaps the Bill needs to specify categories of measuring products and
have different requirements for each.

Hanlie

> Date: Fri, 01 Nov 2013 12:27:21 +0200
> From: Peter Newmarch <newmarch at land-surveyors.com>
> Subject: [OSGeo Africa] Is a map a measuring product ?
>
> Dear all,
>
> Having recently commented on the Legal Metrology bill with regards
> measuring services, I am now applying my mind to a measuring product -
> Is a map a measuring product ? (you can certainly measure things off the
> map).
>
> Also what are your thoughts about that fact that any incorrect statement
> will be a crime - 10 years in jail. ?
>
> If the map (which can be considered as a statement of reality), is
> incorrect in some way, then you would be criminally charged for this. -
> your thoughts ?
>
> And lastly, if you import (presumably also download into the country) a
> measuring product, you will need to be licensed for this else you are
> committing a crime. In the case of say an infra red image - each pixel
> represents a certain measuring unit or quantity of something - It would
> be a measuring product ?
>
> Your thoughts on this as we need to make sure that the geospatial
> industry gets the best deal it can get under this Bill.
>
> Much appreciated if people can think about this and let me know their
> thoughts.
>
> Regards
>
> Peter
>
> Peter Newmarch
> Professional Land Surveyor
> 4Y GeoInformatics Pty Ltd
> Tel       : +27 31 5642856
> Fax       : +27 31 5643074
> Mobile    : +27 82 5705859
> eMail     : newmarch at land-surveyors.com