Grid Maker and North Arrow
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Sam
Apr 21, 2009, 2:52:13 PM4/21/09
to MapInfo-L
I am making a map using a Peruvian projection and using the tools Grid
Maker and North Arrow. I would like to put both a grid and a north
arrow on the map, but when I use the correct magnetic declination in
the North Arrow tool, it is not parallel to the grid.
There are two ways to explain this. Either the grid is already at the
correct declination and the arrow is calculated off North on the
projection or the arrow is on the correct declination and the grid is
not aligned with true north.
I would appreciate any advice on how to properly display these.
Regards,
Sam
Maker and North Arrow. I would like to put both a grid and a north
arrow on the map, but when I use the correct magnetic declination in
the North Arrow tool, it is not parallel to the grid.
There are two ways to explain this. Either the grid is already at the
correct declination and the arrow is calculated off North on the
projection or the arrow is on the correct declination and the grid is
not aligned with true north.
I would appreciate any advice on how to properly display these.
Regards,
Sam
Gentreau
Apr 21, 2009, 4:42:44 PM4/21/09
to mapi...@googlegroups.com
Isn't this just showing you that True North and Magnetic North are not the
same thing?
Mats Elfström
Apr 21, 2009, 4:44:35 PM4/21/09
to mapi...@googlegroups.com
Hi Sam!
Can't it be that the grid is in fact oriented true north and the adjusted North arrow points to the magnetic north pole?
But here we need to discuss what the north arrow should signify.
In my mind, the geographic north pole has been the one and only option.
If magnetic declination needs to be given on the map, I have seen it visualised as a deviating bearing on a circle section, also stating the exact angle against true north and its date. Because as you know, the declination varies over time.
So I would find it very strange if the grid was oriented on the magnetic declination.
This was an interesting question. Let's hope for more input.
I may be further off the target than your north arrow.
Cheers, Mats.E
Can't it be that the grid is in fact oriented true north and the adjusted North arrow points to the magnetic north pole?
But here we need to discuss what the north arrow should signify.
In my mind, the geographic north pole has been the one and only option.
If magnetic declination needs to be given on the map, I have seen it visualised as a deviating bearing on a circle section, also stating the exact angle against true north and its date. Because as you know, the declination varies over time.
So I would find it very strange if the grid was oriented on the magnetic declination.
This was an interesting question. Let's hope for more input.
I may be further off the target than your north arrow.
Cheers, Mats.E
2009/4/21 Sam <shrik...@gmail.com>
Mike Jamieson
Apr 21, 2009, 7:43:04 PM4/21/09
to mapi...@googlegroups.com
When one uses a UTM projection the only place the grid will be precisely parallel to the north arrow is at the equator and I suppose the exact middle meridian of a UTM zone. As you move north or south the grid will be at some angle to the north arrow ( except on the center meridian of each zone), because the UTM grid is now a rectangular/ orthogonal? representation of a roughly trapezoid shaped area due to the convergence of the lines of longitude as you move closer to the north or south pole or to the east or west extents of the UTM zone.
On published maps from the Canadian government (NAD 27 or NAD83) the grid is typically rotated and as per convention the map is oriented with North at the top. In the far north the Canadian government topographic maps near the boundaries of adjacent UTM zones often show coordinates for both of the adjacent zones.
As Mats pointed out it is common to display both true north and the magnetic north arrows on a map, with the year and the annual variation of the magnetic declination.
Mike
________________________________
On published maps from the Canadian government (NAD 27 or NAD83) the grid is typically rotated and as per convention the map is oriented with North at the top. In the far north the Canadian government topographic maps near the boundaries of adjacent UTM zones often show coordinates for both of the adjacent zones.
As Mats pointed out it is common to display both true north and the magnetic north arrows on a map, with the year and the annual variation of the magnetic declination.
Mike
________________________________
JamesL
Apr 22, 2009, 5:59:52 AM4/22/09
to MapInfo-L
Sam,
The North Arrow tool creates a main arrow labelled 'N' pointing
towards geographic north (ie the north pole). You can then choose
whether to plot an arrow pointing to magnetic north (labelled 'M' by
default) by entering the declination for the appropriate location and
date of the map. As pointed out already, UTM projections (such as the
MapInfo Peruvian set) only have their easting grid lines parallel to
geographic north in the centre of the UTM zone. Towards each edge of
the zone the difference gets progressively larger until, at the very
edge the difference is several degrees (how many degrees depends how
far north or south you are).
To test this out and check for yourself, place a latitude-longitude
grid in your map window and you will see that the main north arrow
created by the tool is parallel to the longitude lines.
There should probably be an additional option in the North Arrow tool
to add 'grid north'. The main north arrow should be labelled 'true
north' for the sake of clarity.
Hope this helps you out
Regards
James
The North Arrow tool creates a main arrow labelled 'N' pointing
towards geographic north (ie the north pole). You can then choose
whether to plot an arrow pointing to magnetic north (labelled 'M' by
default) by entering the declination for the appropriate location and
date of the map. As pointed out already, UTM projections (such as the
MapInfo Peruvian set) only have their easting grid lines parallel to
geographic north in the centre of the UTM zone. Towards each edge of
the zone the difference gets progressively larger until, at the very
edge the difference is several degrees (how many degrees depends how
far north or south you are).
To test this out and check for yourself, place a latitude-longitude
grid in your map window and you will see that the main north arrow
created by the tool is parallel to the longitude lines.
There should probably be an additional option in the North Arrow tool
to add 'grid north'. The main north arrow should be labelled 'true
north' for the sake of clarity.
Hope this helps you out
Regards
James
Message has been deleted
arunas.urbsys
Apr 29, 2009, 4:31:53 AM4/29/09
to MapInfo-L
Hi,
I have posted some replay to this thread discussing the difference of
the True North and Magnetic North arrow, but suddenly discovered, that
the problem discussed is the UTM grid (for Peru) and the rotation of
the True North arrow from the grid. As answered here this rotation has
nothing to do with the Magnetic Declination - you can see the
difference between True North and the Magnetic North if you tich the
checkbox "Display Magnetic Declinatio" in the Magnetic Declination
dialog of the North Arrow tool - the North Arrow image will be drawn
with two North Arrows - one, pointing to Geographic North (denoted by
"N"), and another pointing to the direction of the compass niddle,
when you are at that location (the Magnetic North, denoted by "M").
But the true north of the North Arrow in the UTM grid is pointing to
the Geographic North pole, which is best seen if you put on the same
UTM projection the geographic Longitude/Latitude grid. And as
discussed in this thread, the same way as UTM projection grid differs
from Geographic Lon/Lat grid, the True North Arrow also differs from
the UTM projection grid.
The only ways to deal with North Arrow in this sittuation are either:
a) choose the most correct UTM zone projectio for the particular close
territory of the location - in this case the True North Arrow will be
in parallel to the UTM grid, as the correct UTM zone will be the
closest match of the projection of particular location, or b) use
MapInfo North Arrow tool option (radiobutton) "point north arrow to
top of map" - since UTM grid will be always perpendicular to the map
window, even if the chosen UTM zone projection is not the closest for
the displayed locatin, the North Arrow, pointed to the top of map will
be in parallel to the UTM grid.
Another option - have UTM projection grid and in different color or
scale - geographic grid. The True Nort arrow will then be aligned to
the geographic north in parallel to the geographic grid lines.
Best regards,
Arunas Urbsys
GIS Project Manager
arunas.urbsys(at)gmail.com
I have posted some replay to this thread discussing the difference of
the True North and Magnetic North arrow, but suddenly discovered, that
the problem discussed is the UTM grid (for Peru) and the rotation of
the True North arrow from the grid. As answered here this rotation has
nothing to do with the Magnetic Declination - you can see the
difference between True North and the Magnetic North if you tich the
checkbox "Display Magnetic Declinatio" in the Magnetic Declination
dialog of the North Arrow tool - the North Arrow image will be drawn
with two North Arrows - one, pointing to Geographic North (denoted by
"N"), and another pointing to the direction of the compass niddle,
when you are at that location (the Magnetic North, denoted by "M").
But the true north of the North Arrow in the UTM grid is pointing to
the Geographic North pole, which is best seen if you put on the same
UTM projection the geographic Longitude/Latitude grid. And as
discussed in this thread, the same way as UTM projection grid differs
from Geographic Lon/Lat grid, the True North Arrow also differs from
the UTM projection grid.
The only ways to deal with North Arrow in this sittuation are either:
a) choose the most correct UTM zone projectio for the particular close
territory of the location - in this case the True North Arrow will be
in parallel to the UTM grid, as the correct UTM zone will be the
closest match of the projection of particular location, or b) use
MapInfo North Arrow tool option (radiobutton) "point north arrow to
top of map" - since UTM grid will be always perpendicular to the map
window, even if the chosen UTM zone projection is not the closest for
the displayed locatin, the North Arrow, pointed to the top of map will
be in parallel to the UTM grid.
Another option - have UTM projection grid and in different color or
scale - geographic grid. The True Nort arrow will then be aligned to
the geographic north in parallel to the geographic grid lines.
Best regards,
Arunas Urbsys
GIS Project Manager
arunas.urbsys(at)gmail.com
Tim Rideout
Apr 29, 2009, 6:20:17 AM4/29/09
to MapInfo-L
In the MAPublisher plugin for
Adobe Illustrator you can do a live play about with the north arrow. Once you
have inserted a north arrow then the object aligns itself to point at true
north, wherever that is in the current projection. If you select the north arrow
object and then drag it about the screen it will then rotate as you move in
order to stay pointing at north. In the GB National Grid (a Transverse Meractor,
but not UTM) this means that on the projection centre (2 degrees west) the arrow
points straight up, as you drag it west it gradually tips to point more to the
right, as you drag it east it gradually tips to point more to the left. All in
all it is quite fun to just wiz it about and see what the effect
is.
regards
Tim
Dr Tim Rideout
The XYZ Digital Map
Company
Subject: [MI-L] Re: Grid Maker and North Arrow
scale - geographic grid. The True Nort arrow will then be aligned to
the geographic north in parallel to
the geographic grid lines.
Best regards,
Arunas Urbsys
GIS Project
Manager
arunas.urbsys(at)gmail.com
On Apr 22, 12:59 pm, JamesL
<ja...@natmin.com> wrote:
Sam
Apr 29, 2009, 6:59:16 PM4/29/09
to MapInfo-L
Hi folks!
Thanks for all the useful information. You answered my question about
how the north arrow works and then some. This will be very useful.
Cheers,
Sam
Thanks for all the useful information. You answered my question about
how the north arrow works and then some. This will be very useful.
Cheers,
Sam
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