[GIS] Overlaying lat/long graticules on projected map using QGIS

grids-graticuleslatitude longitudeqgis

I am using an equal areas projection of North America and would like to overlay a lat/long grid.

I can do this in the print composer, but only for the coordinates.

Can QGIS do a distorted grid for lat/long coordinates over a projected map? If so, how?

Best Answer

Not built in , AFAIK. The way I do this is by creating a polygon shape file "grid" and then reprojecting it. So you could:

enable On-the-fly reprojection
Set the CRS to Lat/Lon
Use the Vector->Research Tools->Vector Grid to create a polygon grid at whatever interval is appropriate
Display the polygons with no fill, to show only the grid lines.
Return to your projected CRS, but keeping on the fly reprojection.

Now the Lat/Lon grid lines will display "distorted". If you also want to show coordinate labels on the grid lines, maybe this (somwhat old) post will be helpful.

Related Solutions

[GIS] Adding graticules to the edge of the map only in QGIS

It is possible to get tick marks just along the edge of the map object's frame, just a little fiddly:

Check 'Show Grid' in the map's Item Properties.
Set the grid interval to whatever you want (some multiple of your real world units e.g. 1,000m or whatever). This will give you a complete grid, but don't worry - we'll fix that...
Set 'Frame Style' to 'No Frame' (default).
Click on 'Line Style' to get the Symbol Selector dialog. On the left-hand side of the dialog note the 'Symbol layers' pane.
Select the item labelled 'Simple Line' and click the 'Symbol layer type' drop-down list on the top right (currently also set to 'Simple Line') and change it to 'Marker Line'. You will get a load of red dots.
In 'Marker Placement' select 'on last vertex only'.
Back in the Symbol layers pane, select the item marked 'Simple marker' (expand the 'Marker Line' item if necessary using the little + next to it). Change the marker to a vertical line and set its angle to 90 degrees (this is important).
You are now halfway there (trust me!). Go back to the 'Symbol layers' pane and click on the very first item 'Line' (the parent in the symbol hierarchy). This enables the grey-out plus button at the bottom of the dialog box, turning it green. Press the green + button.
Now repeat the steps above except this time choose 'on first vertex only' in step 6. When you are done click OK at the bottom right.

You should now have tick marks on just the edge of the map object's frame. You can change the size and thickness of the by going to Simple Marker item (last item at the bottom of each of the 'Marker line' hierarchies) and playing with 'Size', 'Colors' and ;Outline width' etc to make it look how you want.

As you have discovered, the map frame works by automatically clipping everything to its limits, this means that you can only have the tick marks pointing inwards, unless you get even more devious! To get them pointing out do this:

Create a second map object and using the position and size controls, set it to exactly the same size and position as the map object with the tick marks. (it will temporarily cover it).
You now need to align the data. Set the extents of the new map to match your original one. Make a note of the scale.
Go to 'Position and size' and set the reference point to be the middle of the new map. adjust the Width and height so that the new map fits neatly within the tick marks of the first one. Do NOT pull the map manually with the handles.
Your extent and scale will now have changed on the new map. Set ONLY the scale to the value you noted in step 2.
Check 'Lock layers for map item' on the new map object.
Switch back to main QGIS window and turn off all your layers until the canvas is blank.
Switch back to the Map Composer and check 'Lock layers for map item' on the original map object (the one with the tick marks.

You now should have a map window showing your data and tick marks on the outside. You can go ahead and turn your layers back on now without upsetting your arrangement because you locked the layers of the tick-map item. I think it looks goof to add a frame to the inner map object (not with map's 'Show grid' but with the standard 'Frame' option towards the bottom of the Item properties controls.

[GIS] Converting local Coordinates to lat/long Coordinates using QGIS

You have to build the proj.4 string for the CRS from the parameters given:

+proj=lcc +lat_1=44.883333 +lat_2=45.133333 +lat_0=44.791111 +lon_0=-93.383333 +x_0=152400.000000 +y_0=30480.000000 +a=6378418.9409999996 +b=6357033.3098455509 +towgs84=0,0,0,0,0,0,0 +units=us-ft +no_defs

Note that x_0 and y_0 have to be in meters, while false Easting and Northing from the definition (and the WKT mkennedy added) are in units of the projection (us-ft).

With that, you can load the data as delimited text, with X set to the itm column and Y to the utm column. If you have not set QGIS to prompt for the CRS, rightclick on the layer -> Set CRS for layer

to get the right alignment:

enter image description here

I'm not sure why they have named the second column utm, the projection has nothing to do with Universal Tramnsverse Mercator.

Best Answer

Related Solutions

[GIS] Adding graticules to the edge of the map only in QGIS

[GIS] Converting local Coordinates to lat/long Coordinates using QGIS

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