Tutorial: Side-by-Side Maps in QGIS Print Composer

Step #1: Open New Print Composer

QGIS print composer can be a bit daunting and confusing. It is equivalent to the Layout View in ArcGIS, where users can setup their map for printing and publication. One common task is to create side-by-side maps, to compare imagery, choropleth, or other types of maps.  I looked but could not find a good tutorial with screenshots, so here we go!

Purpose

To create three side-by-side maps of different band combinations from Landsat 7 imagery of the Salton Sea. The maps will be exactly the same size.  The different band combinations were created using the Orfeo Toolbox->Image Manipulation->Images Concatenation and selecting various band combinations.

Step #1:  For starters...

I've started by just selecting the natural color view (bands 3-2-1).  Go to the the Project Toolbar in the upper left-> New Print Composer. 

• You can also can the page layout to landscape or portrait, depending on whether your map series will be laid out horizontally or vertically.

Step #2:  Creating the first map

Click the "Add New Map" button, highlighted in red. and draw an area for your map on the blank page.  For best fit of your image, be sure in QGIS to have zoomed into an area of interest. 

• Then on the right hand side of print composer, select "Item Properties" and click the long button for "Set to Map Canvas."

After Steps #1-2

Step #3: Add the second map

Before adding the second map to the right, scroll up in "Item properties" and check the box for "Lock layers for map item."  The click on the existing map in print composer and copy and paste it. On this second map, be sure to uncheck the box we just checked: Uncheck "Lock layers for map item."

• In QGIS, add the next layer, in this case I added a false color image from bands 4-3-2.
• Go back into Print Composer and hit the blue refresh button.
• The second map should display the false color image and the first map should remain natural color.

After Step #3

Step #4: Repeat for the third map

Before copying and pasting, make sure to check the "Lock layers for map item" box.  Copy, paste, and then uncheck this for the third map, with the last set of band combinations (7-4-2).  The final map appears below.

Click to enlarge the map.
Three side-by-side maps, equal sized, and the same scale.

For more information:

You can find additional tips about using the map composer from multiple frames and different layers in this discussion on StackExchange: http://gis.stackexchange.com/questions/45174/how-to-handle-multiple-map-frames-with-different-layers-in-one-print-layout

What to Expect in QGIS 2.10 Pisa

With the next release of QGIS on the horizon, I downloaded the latest nightly build and looked through the visual change log to see what to expect.  What I found is very exciting!

If you have not looked at QGIS Visual Change Log, it is a quick way to see changes from release-to-release.  It includes screenshots and quick explanations of the upcoming changes.  It also lists the contributor(s) and funding source.

Rasters
The new release includes log functions (natural and base 10) for the raster calculator.  This is great since many remote sensing calculations use logs, for example land surface temperature via Landsat 8. Zonal Statistics for rasters is now included as a core plugin of QGIS.  This allows users to summarize the characteristics of raster layers using a polygon layer for setting zones.

Symbology and Histograms
When you go to symbolize a layer using a graduated scheme, you can now adjust the breaks by using an interactive histogram, akin to what you will find in ArcGIS.  If you change your classification scheme, be sure to (re)load or reclassify the layer before clicking on the histogram tab.  Below is quick example using population by county for Maryland.

Histogram view of two classification schemes:
Top: Equal interval, Bottom: Quantile / Equal Count

Live layer effects
Live layer effects is probably the most talked about new feature and was crowd-sourced.  It adds the ability for a variety of effects including a drop shadow.  The creator of this feature has a great post and quick how-to. Basically, when you got to style a layer, look towards the bottom, check the "Draw Effects" check-box.  Then, look a fair way to your right and click the 'yellow star.'

I found using this to be much easier-to-use than its implementation in ArcGIS.

It can be easy to overlook the Draw Effects check box when styling.

Adding effects is easy-to-do in QGIS and look good!

Often, I feel my maps can get stale, or someone wants a more 'graphic' or photo-shopped look for a presentation, other product, or to develop a 'brand.' So having this feature is great, especially, if like me, you are not an expert graphic designer or cartographer. I look forward to seeing creative uses of this feature in the QGIS Flickr Map Showcase.  There may already be a few in there!

Follow point labeling
Good, clear, and legible labeling help separate the good mappers from the bad.  Follow point labeling has been added to align text based on where the label is located.  So, if a label appears to the left of a point, the text will be right-aligned.  This will also help with multi-line labels.

True Curves
There is a new geometry engine which allows for 'true curves' to be represented as such -- instead of segmented lines or polygons.  If I am not mistaken, I believe this is very important for a variety of users, but particularly for CAD users or those that use CAD and GIS.

New desktop icon
To start QGIS, the old familiar neon yellow/green "Q" is gone in favor of a more professional looking two-tone green globe for an icon.  I am glad that the distinctive QGIS green remains,  For those using both ArcGIS and QGIS installed on the same computer, it will still be easy to distinguish between the program icons.

An Epic View with NASA's Worldview

In an ever-changing world, having a global view is extremely important.  NASA has developed several website/tools where you can view and download up-to-date global remote sensing data.  NASA's Worldview is one of them.  If you are looking for a quick example of its practical value, take a look at last fall's forest fires in the western U.S.

 "Most of the 100+ available products are updated within three hours of observation, essentially showing the entire Earth as it looks 'right now'. This supports time-critical application areas such as wildfire management, air quality measurements, and flood monitoring."- NASA Worldview Website

Of note, browsing on a tablet or smartphone is supported.  There is a layered slider for time, so users can choose the year, month, and day. Selecting dates in some websites can be painful.  However, this slider is intuitive, quick, and easy to use--much more so than those pesky calendar pages some users are forced to navigate.  Users also have several base maps to choose from in addition to the rest of the layers.  There is a great "About" page and brief "Tour" available.

Global Land Surface Temperatures/Day from MODIS, 17 July 2013

A few basic social features are built-in.  The website has buttons for saving links to certain views and taking screenshots.  There are lot of different instruments and views but everything is well-labeled. A few different band combinations can be selected with one-click for easy viewing.  This is especially important for looking at vegetation and agriculture, for example. 

You can also check out recent scenes from Landsat 7 at: http://earthnow.usgs.gov/ or Landsat 8 at: http://landsatlook.usgs.gov/.  If you are interested in NASA's open data policies, a quick overview can be found at: http://science.nasa.gov/earth-science/earth-science-data/data-information-policy/

'Continuing the Landsat Legacy'

Barring anything unforeseen, the next Landsat satellite should liftoff in early 2013.  NASA has an interesting Twitter page of announcements and opportunities for the wide range of its users. In addition, a recent full free issue of Remote Sensing and the Environment contained lots of articles about the exciting past, present and, future of the Landsat program. A cool brochure is also available. Be sure to check it out! When it comes to free data, Landsat has to come to your mind! 


Comparison of Landsat Satellites -- What's Ahead... (Click on the Image to Enlarge)

Viva Landsat over Las Vegas

The Landsat mission tracks changes in land cover over Las Vegas in the video below.  The compilation was released about one week ago but is still fun to look at.  The Landsat mission may receive an extra boost, already well exceeding its lifetime, if the Landsat 5 satellite comes back online.  The next Landsat mission is expected to begin sometime in 2013.