So following up from Creating Maps in QGIS,
today we’ll discuss using the Atlas Panel in the Print Layout to rapidly generate multiple
maps. The Atlas panel uses a specified ‘Coverage
Layer’ to define the geographies of the outputs. Today we’ll use it to map population dynamics
in Census Metropolitan Areas - or CMAs for short - across Canada - effectively semi-automating
the map production process. So once again the preparation steps are provided
in the video description – but to summarize quickly, we used the one-to-one join procedures
to link the population table to the Census Tract layer. The Refactor Fields tool was then applied
to save to a permanent file with correctly attributed field types. We also dissolved the Census Tract layer using
the Census Metropolitan Area Name (CMANAME) field to create the Coverage Layer for our
Atlas, and with the fill colour set to fully transparent, outline the Census Tracts within
our main map group. The cartographic Census Subdivision layer
was then run through the Fix Geometries tool, dissolved by the Provincial Unique Identifier
and run through the Multipart to Single Part tool, ensuring that all features were separate
entries within the attribute table. Area fields were added to it, and the Lakes
and Rivers polygon, using the Field Calculator and the Select by Expression tool used to
subset features with areas greater than 2500 and 500 square kilometres respectively and
grouped together to comprise our Inset Map. The Labels applied to our coverage and province
layers had similar settings. So to quickly summarize – in the Formatting
subtab for the coverage Layer we specified to wrap text on the dash character. A text buffer was also applied – with the
coverage layer set to 75% Opacity. The Placement was set to Horizontal (slow)
ensuring the legibility of the text-based labels. And in the Rendering tab only draw labels
which fit completely within the feature was checked and discourage labels from covering
the feature’s boundaries was selected with the highest weight applied. So now we can toggle off the Prep Layers group. Now in the Print Layout I used the add shapes
tool, specifically Add Rectangles, to divide the layout for the map items, which were then
locked within the Items panel. The alignment tool on the Actions toolbar
was then used to ensure that added items were placed above the rectangles. I’ve also already added many of the mandatory
map items – including the additional information, scale bar, legend and title. The title uses an expression, including a
generic text prefix within single quotes followed by the vertical separators and then Census
Metropolitan Area name field to label by metropolitan area, which will update automatically once
our Atlas is generated. Just a quick tip for map item formatting - if
greater control was needed – the Print Screen or Snipping tools could be used to export,
externally format and re-add items, such as the legend, diagrams or table, as a picture. On that note our North Arrow is still missing. So rather than using the add Arrow and Text
label function, let’s add it from Picture this time. Clicking and dragging across the desired location
in the Print Layout, we can then go to the Item Properties Panel and expand the Search
Directories. And once loaded select the desired icon. I’ll alter the Fill Colour to be darker,
to ensure its visibility against the main map, and then clicking Back, we’ll also
switch the placement to Middle. So now we can add both maps simultaneously
– placing the main map in the larger box of the layout and the inset map in the smaller
box on the right. The main map is currently being rendered over
our north arrow, so once again we’ll select it and use the Lower in the Alignment tools
to ensure the north arrow is visible. While they’re rendering I’d also like
to highlight that the scale-bar for the main map is set to Fit Segment Width as opposed
to the Fixed Width used in the previous demo, which will update the scale-bar according
to the size of the census metropolitan area being mapped. Now for our second map, let’s add a Grid,
expanding the drop-down and clicking the Plus icon – and then select Modify Grid Properties. We’ll also change the CRS to WGS 84, entering
4326 in the system selector, so that we can show coordinates in decimal degrees. We’ll specify an interval of 2 degrees,
which at the moment adds many lines, but will be more appropriate once we generate the Atlas. Check the Draw Coordinates button. The format of the coordinates can then be
selected in the drop-down, here we’ll leave it with the default. We’ll specify to show latitude only for
the Right and Left parameters and longitude only for the Bottom and Top. At the bottom of the panel we’ll change
the precision for the Grid units to 1. Back in the Item Properties Panel for the
Inset Map, we’ll also add an Overview – clicking the plus icon and specifying the map being
overviewed in the drop-down, which is Map 1. Now we can generate the Atlas. So in the Atlas drop-down on the Menu-bar
select Atlas Settings. And within the Atlas panel check Generate
Atlas and specify the Coverage Layer – in this case DCMAAtlas or the dissolved Census
Metropolitan Areas. We’ll specify the field used for the Page
Name, in this case the CMANAME field and use the same field for Sort by. This will sort them alphabetically when we
preview our Atlas. Uncheck the Single Export option, as we want
each metropolitan area to be a separate map and select the desired output file format. Additionally we’ll change the output filename
to something more intuitive than just the feature IDs. So we’ll switch ‘Output’ to JCTPop and
then click on the Expression box. In the Variables drop-down, we will replace
featureID with @atlas_pagename, which we set to CMANAME field, so the outputs will be named
according to the census metropolitan area. This did involve a trade-off– requiring
the entries within the CMANAME field to be reformatted - removing periods, slashes, question
marks and other symbols that caused erroneous filenames, which would lead to the atlas output
failing. So having replaced these characters I can
just click OK. Now we can Select Map 1 and within the Item
properties Panel check the Controlled by Atlas box. For the main map we’ll specify 5% for the
Margins Around the Feature. In the main interface we can now toggle off
the inset map group. And back in the Print Layout select the main
map and in the Item Properties Panel check Lock Layers and Lock Styles. Repeating with Map 2, we’ll check controlled
by Atlas once again and enter a larger margin of 750% to ensure the broader geographic location
is shown. Then in the main interface toggle off the
main map group and back in the layout select Lock Layers. And this is so that the inset map does not
show the layers of the main map and vice versa. Now on the Atlas toolbar we can select the
Preview Atlas icon. So we can toggle through the different CMAs
alphabetically, or select ones of interest from the drop-down. The next metropolitan area is Barrie. So as you can see, the title, grid and scale-bar
update rapidly, while the maps, particularly the Inset Map takes longer. This is likely due to the detail of the cartographic
boundary file, combined with the broader extent being mapped within the inset. I ran the Atlas output earlier – as we can
see scrolling through the maps, most are appropriately formatted and ready for use as supporting
figures or stand-alone documents. Relatively few maps require manual editing
and individual export to maintain intuitive values for map items such as the scale or
grid intervals. For example, for Edmonton we would want to
use a larger interval for the Grid coordinates, such as 5°. And similarly, for Granby, we would want to
alter the scale to Fixed Width and enter 10 for a more intuitive break value. Then we could use the export procedures from
the making maps demo to individually export these specific maps. On the whole, the Atlas Panel has facilitated
rapidly mapping multiple locations and variations in attributes of interest with relatively
little input or effort. Toggling back we could now select another
CMA of interest, such as Drummondville – or one of the outputs from the Atlas that needed
edits such as Edmonton. Then we could select the Inset map, re-expand
the Grids drop-down and click the Modify button – updating the Grid Interval for X to 5
degrees. We could then resize the North Arrow to ensure
it’s not obscuring the main map features, and then individually export this map using
the procedures covered in the previous demo. So with the Export Atlas tool we can specify
the for..file format to use. The same formats from the single export options
are available. It is a good idea to create a separate directory
for the output maps. Then specify the output resolution and click
Save to run. We won’t actually run the output as it’s
a time-intensive process, taking around 35 minutes. The last thing that we would want to do is
save the print layout as a template for further use, such as reapplying for map production
in the next census collection period or to generate maps with a different variable of
interest at the Census Tract level. So use the Atlas panel with a coverage layer
to rapidly and easily generate multiple maps for particular areas of interest. Save the template for re-use in examining
other variables of interest or applying in another time-period. Apply these skills to your own areas of expertise
and datasets of interest for semi-automated map production.
