[OpenMap Users] General map questions: Shifting points ... strange

Hello everybody,

I have some questions about a more general topic not particularily about
OpenMap.

Background: I have a picture of a map which I have with some effort geocoded
using reference points. I have some locations to map to this map. I geocoded
those location using a internet mapping service which provides WGS84
locations. I used the same service for the reference points for putting the
map at hte place.

Now, I added the first location point provided as longitude latitude in
WGS84 to my map and it was fine. However when I added more points I realised
that there were shifted somehow. Now my questions (Qx):

Q1: How can the points be shifted, even it I use the same mapping service
for putting the map picture in place and geocoding the location points. It
is both the same coordinate system (WGS 1984).

Q2: In general, what are reasons for that effect that points shift even
though the same system is used, BUT different maps.

Q3: Does anybody know how this problem is officially called and where I can
specifically read more about it (want to write about it and need therefore
more information).

Q4: Does somebody know more general mailing lists where I can ask questions
about mapping in general (geocoding, mapping, technologies related with the
mapping business etc.) ?

Thank you very much for your help,
Karl Koch

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