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Wed Aug 24 18:10:12 2016

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City flows unfolding with the other Processing

A previous version of this post has been published in German on Die bemerkenswerte Karte.

Visualizations of mobility data such as taxi or bike sharing trips have become very popular. One of the best most recent examples is cf. city flows developed by Till Nagel and Christopher Pietsch at the FH Potsdam. cf. city flows visualizes the rides in bike sharing systems in New York, Berlin and London at different levels of detail, from overviews of the whole city to detailed comparisons of individual stations:

The visualizations were developed using Unfolding, a library to create interactive maps and geovisualizations in Processing (the other Processing … not the QGIS Processing toolbox) and Java. (I tinkered with the Python port of Processing in 2012, but this is certainly on a completely different level.)

The insights into the design process, which are granted in the methodology section section of the project website are particularly interesting. Various approaches for presenting traffic flows between the stations were tested. Building on initial simple maps, where stations were connected by straight lines, consecutive design decisions are described in detail:

The results are impressive. Particularly the animated trips convey the dynamics of urban mobility very well:

However, a weak point of this (and many similar projects) is the underlying data. This is also addressed directly by the project website:

Lacking actual GPS tracks, the trip trajectories are rendered as smooth paths of the calculated optimal bike routes

This means that the actual route between start and drop off location is not known. The authors therefore estimated the routes using HERE’s routing service. The visualization therefore only shows one of many possible routes. However, cyclists don’t necessarily choose the “best” route as determined by an algorithm – be it the most direct or otherwise preferred. The visualization does not account for this uncertainty in the route selection. Rather, it gives the impression that the cyclist actually traveled on a certain route. It would therefore be undue to use this visualization to derive information about the popularity of certain routes (for example, for urban planning). Moreover, the data only contains information about the fulfilled demand, since only trips that were really performed are recorded. Demand for trips which could not take place due to lack of bicycles or stations, is therefore missing.

As always: exercise some caution when interpreting statistics or visualizations and then sit back and enjoy the animations.

If you want to read more about GIS and transportation modelling, check out
Loidl, M.; Wallentin, G.; Cyganski, R.; Graser, A.; Scholz, J.; Haslauer, E. GIS and Transport Modeling—Strengthening the Spatial Perspective. ISPRS Int. J. Geo-Inf. 2016, 5, 84. (It’s open access.)


Special FOSS4G offer: 25% off QGIS Map Design

FOSS4G2016 is drawing closer quickly. To get in the mood for a week full of of geogeekery, Locate Press is offering a special FOSS4G discount for QGIS Map Design.

Use the code foss4gbonn to get 25% off your copy.

QGIS Map Design is the reference book to get if you want to bring your mapping skills up to speed. The book comes with a download for all our example map projects:

qmd78 qmd34 qmd108 qmd140 qmd52 qmd168 qmd132 qmd84 qmd90 qmd120 qmd184 qmd174 qmd188 qmd46 qmd128 qmd158 qmd20 qmd114 qmd180 qmd100 qmd146 qmd26 qmd152 qmd164 qmd104 qmd58 qmd64

Looking forward to meeting you in Bonn!


OSM turn restriction QA with QGIS

Wrong navigation instructions can be annoying and sometimes even dangerous, but they happen. No dataset is free of errors. That’s why it’s important to assess the quality of datasets. One specific use case I previously presented at FOSS4G 2013 is the quality assessment of turn restrictions in OSM, which influence vehicle routing results.

The main idea is to compare OSM to another data source. For this example, I used turn restriction data from the City of Toronto. Of the more than 70,000 features in this dataset, I extracted a sample of about 500 turn restrictions around Ryerson University, which I had the pleasure of visiting in 2014.

As you can see from the following screenshot, OSM and the city’s dataset agree on 420 of 504 restrictions (83%), while 36 cases (7%) are in clear disagreement. The remaining cases require further visual inspection.

toronto_turns_overview

The following two examples show one case where the turn restriction is modelled in both datasets (on the left) and one case where OSM does not agree with the city data (on the right).
In the first case, the turn restriction (short green arrow) tells us that cars are not allowed to turn right at this location. An OSM-based router (here I used OpenRouteService.org) therefore finds a route (blue dashed arrow) which avoids the forbidden turn. In the second case, the router does not avoid the forbidden turn. We have to conclude that one of the two datasets is wrong.

turn restriction in both datasets missing restriction in OSM?

If you want to learn more about the methodology, please check Graser, A., Straub, M., & Dragaschnig, M. (2014). Towards an open source analysis toolbox for street network comparison: indicators, tools and results of a comparison of OSM and the official Austrian reference graph. Transactions in GIS, 18(4), 510-526. doi:10.1111/tgis.12061.

Interestingly, the disagreement in the second example has been fixed by a recent edit (only 14 hours ago). We can see this in the OSM way history, which reveals that the line direction has been switched, but this change hasn’t made it into the routing databases yet:

now before

This leads to the funny situation that the oneway is correctly displayed on the map but seemingly ignored by the routers:

toronto_okeefe_osrm

To evaluate the results of the automatic analysis, I wrote a QGIS script, which allows me to step through the results and visually compare turn restrictions and routing results. It provides a function called next() which updates a project variable called myvar. This project variable controls which features (i.e. turn restriction and associated route) are rendered. Finally, the script zooms to the route feature:

def next():
    f = features.next()
    id = f['TURN_ID']
    print "Going to %s" % (id)
    QgsExpressionContextUtils.setProjectVariable('myvar',id)
    iface.mapCanvas().zoomToFeatureExtent(f.geometry().boundingBox())
    if iface.mapCanvas().scale() < 500:
        iface.mapCanvas().zoomScale(500)

layer = iface.activeLayer()
features = layer.getFeatures()
next()

You can see it in action here:

I’d love to see this as an interactive web map where users can have a look at all results, compare with other routing services – or ideally the real world – and finally fix OSM where necessary.

This work has been in the making for a while. I’d like to thank the team of OpenRouteService.org who’s routing service I used (and who recently added support for North America) as well as my colleagues at Ryerson University in Toronto, who pointed me towards Toronto’s open data.


One “add” button to rule them all

Reducing the number of “Add layer” buttons in the QGIS GUI is a commonly voiced wish. Multiple approaches have been discussed but no decision has been made so far. One idea is to use the existing browser functionality to replace the “Add layer” dialogs. Others are envisioning completely novel approaches.

Since the topic came up again today on Twitter, I decided to implement a quick & dirty version of a unified Add layer button. This way, I can comfortably reduce my Layer toolbar to three buttons using Settings | Customization …

layerToolBar

customization

I pretty much just kept the “Create new layer” button and the “Add delimited text layer” button because, as far as I know, there is no way to call the dialog from the browser. (Instead, CSVs are opened with OGR, which doesn’t have nearly as many nice features.)

And here it is in action:

(I recommend to undock the Browser panel to get the dialog-like behavior that you see in the video.)

To install the plugin: download it and unzip it into your QGIS plugin folder, then activate it in the plugin manager.

I would love to hear what you think about this UX experiment.


Slides & workshop material from #QGISConf2016

If you could not make it to Girona for this year’s QGIS user conference, here’s your chance to catch up with the many exciting presentations and workshops that made up the conference program on May 25-26th:

(Some resources are still missing but they’ll hopefully be added in the coming days.)

Update: Now you can also watch the talks online or even download them.

Thanks to everyone who was involved in making this second QGIS user conference a great experience for all participants!


Traveltime routing & catchment extension for the QGIS IDF router

As announced in Salzburg a few days ago, I’m happy to present the lastest enhancement to my IDF router for QGIS: travel time routing and catchment computation.

Travel times for pedestrians and cyclists are computed using constant average speeds, while car travel times depend on the speed values provided by the road network data.

Catchment computations return the links that can be traversed completely within the given time (or distance limit). The current implementation does not deal with links at the edge of the catchment area, which can only be traversed partially.

Loading the whole network (2.7GB unzipped IDF) currently requires around 10GB of memory. One of the next plans therefore is to add a way to only load features within a specified bounding box.

Plans to turn this into a full-blown plugin will most likely have to wait for QGIS 3, which will ship with Python 3 and other updated libraries.

Screenshot 2016-07-17 22.04.54


Exploring CKAN data portals with QGIS

CKAN is for data portals what QGIS is for GIS. The project describes itself as

CKAN is a powerful data management system that makes data accessible – by providing tools to streamline publishing, sharing, finding and using data. CKAN is aimed at data publishers wanting to make their data open and available.

Many open (government) data platforms rely on CKAN and while the web interface is pretty good, there’s still the hassle of finding and downloading the data using a web browser.

This is where the QGIS CKAN-Browser plugin comes in useful. The plugin has been developed by BergWerkGIS for the state of Carinthia, Austria and added to the public plugin repo earlier this year. CKAN-Browser comes preconfigured with some Austrian and European CKAN URLs for testing, so you can get going really quickly. It is easy to search for specific datasets or explore the portal’s data categories and it is just one click to download and load the data into your QGIS map:

Screenshot 2016-06-26 22.25.00

Here’s a quick demo of loading a vector dataset as well as raster tiles:

For the full usage guide, visit the plugin’s Github page.

It’s great to see how well CKAN and QGIS can play together to enable seamless access to open data!


QGIS workshops at FOSSGIS

We are looking forward to a hot geo summer here in Central Europe with both the German FOSSGIS (this year in conjunction with the annual AGIT conference) and the international FOSS4G just a few weeks away. It’s going to be exciting, and I still have a lot of talks (and a keynote) to prep for both events ;-)

If you speak German and want to enhance your geo skills, the FOSSGIS program offers some great opportunities and there is still the chance to sign up for a couple of great FOSSGIS workshops:

Of course the program also features many non-QGIS workshops. If I’d have to pick one of them, it would most certainly be Marc Jansen’s and Andreas Hocevar’s OpenLayers 3 workshop because it’s always great to get the latest information first hand, directly from the developers.

Online registration closes on June 25th.


Videos and slides from FOSSGIS & AGIT OSGeo Day

Last week I had the pleasure to attend the combined FOSSGIS, AGIT and GI_Forum conferences in Salzburg. It was a great joint event bringing together GIS user and developers from industry and academia, working with both open source and commercial GIS.

I was particularly impressed by the great FOSSGIS video team. Their tireless work makes it possible to re-watch all FOSSGIS talks (in German).

I also had the pleasure to give a few presentations. Most of all, it was an honor to give the AGIT opening keynote, which I dedicated to Open Source, Open Data & Open Science.

In addition, I also gave one talk related to an ongoing research project on pedestrian routing. It was really interesting to see that other people – in particular from the OSM community – also talked about this problem during FOSSGIS:

(For more details, please see the full paper (OA).)

To wrap up this great week, Astrid Emde, Andreas Hocevar, and myself took the chance to celebrate the 10th anniversary of OSGeo during AGIT2016 OSGeo Day.

And last but not least, I presented an update from the QGIS project with news about the 3.0 plans and a list of (highly subjective) top new features:


How to create round maps in Print Composer

If you follow me on Twitter, you’ve probably seen previews of my experiments with round maps. These experiments were motivated by a recent question on GIS.stackexchange whether this type of map can be created in QGIS and while it’s not very convenient right now, it is definitely possible:

http://www.quantarctica.org

All maps in this post are created using data from the Quantarctica project.

I’ve been planing to try the Quantarctica datasets for a long time and this use case is just perfect. When you download and open their project, you’ll see that they have already clipped all datasets to a circle around Antarctica:

Quantarctica project with some custom styling

Quantarctica project with some custom styling

Since the map of the full extent of the dataset is already clipped to a circle, the overview map is easy to deal with. The detail map on the other hand is rectangular by default:

circle_maps_start

Since we cannot change the shape of the map item, we have to use a mask instead. To create a circular mask, we can add an ellipse shape:

circle_maps_addellipse

The main challenge when creating the mask is that there is no inverted polygon renderer for shapes in print composer. I’ve evaluated to workarounds: First, I created a style with a wide white outline that would cover all map parts outside the circle shape. But this solution slowed the print composer down a lot. An alternative, which doesn’t suffer from this slowdown is using draw effects:

circle_maps_mask_style

In particular, I created a big outer glow effect:

circle_maps_mask_style_effect

Note that the effect only works if the symbol itself is not transparent. That’s why I set the symbol fill to black and used the Lighten blending mode:

circle_maps_mask

Voilà! Both maps appear are nicely circular.

It is worth noting though that this workaround has a downside: it is not possible to create automatic grids/graticules for these maps. The graticule in the overview map only works because it is a layer in the main project that was already clipped to the circular shape.

Finally, you can add more depth to your map by adding shadows. To create the shadow effect, I added additional ellipse items which are styled with a drop shadow draw effect. If you only enable the drop shadow effect, you will notice that the shadow is cut off at the ellipse bounding box. To avoid this undesired effect, you can add a transform effect, which reduces the size of the drawn shape and it’s shadow so that the shadow fits into the bounding box:

circle_maps_mask_shadow_effect

It requires some manual adjustments to place the shadow at the optimal location on top of the mask:

circle_maps_mask_shadow

Add another ellipse to create the shadow for the overview map.

For more cartography tips and tricks check my new book QGIS Map Design or join my QGIS training courses.


Interview: QGIS in journalism

Last year, I published the short post QGIS on the rise with journalists showcasing how QGIS is used by journalists with examples from the Los Angeles Times and Financial Times.

The latest QGIS case study now features an interview with Steven Bernard (Interactive Design Editor at the Financial Times) by A. Neumann and T. Sutton.

QGIS is now an integral part of our mapping workflow. (…) I would say 80% of our maps are now produced in QGIS. read more …

It’s great to see all the great examples of QGIS used to communicate international news. Thanks to everyone involved in this interview for sharing this case study with the community!


Learning QGIS 3rd ed. discounts

In time for QGIS 2.14 (soon to be LTR), I have updated “Learning QGIS” to reflect the latest improvements of our favorite GIS.

To celebrate, we are giving away 100 copies of the book at 30% (for print) and 50% (for eBook) discount if you use the following codes:

30% off  the Print version
Code: prt30LeaQS

50% off the eBook version
Code: LeaQSebok50

(Codes are valid until 30th April 2016 or we’ve reached 100 copies.)

B05278_MockupCover_Normal


New demos: live labels & gradient editor

Following up on last week’s post, Nyall has continued his work on the QGIS gradient editor:

Latest version of the new QGIS interactive gradient edit. This now includes an interactive plot of the color hue/saturation/lightness/alpha, allowing a visual overview of these color components and easy editing.

Another equally awesome demo has been posted by Nathan, who is currently working on usability improvements for labeling and styling without blocking dialogs:

This is going to be great for map design work because it makes many complex styles much easier to create since you can interact with the map and attribute table at the same time.

These are definitely two developments to follow closely!


Towards better gradients

Interesting developments going on if you like creating your own gradients. After all, that’s not as easy as it might initially seem, as Gregor Aisch describes in his post “Mastering Multi-hued Color Scales with Chroma.js”:

The issues with simple color interpolations, which include nonuniform changes in lightness between classes, also haunt us in cartography. Just have a look at the map and legend on the left-hand side, which has been created using a normal custom QGIS gradient with colors ranging from black to red, yellow and finally white. We end up with three classes in yellow which are nearly impossible to tell apart:

comparing_ramps

For comparison, on the right side, I’ve used Gregor’s corrected color ramp, which ensures that lightness changes evenly from one class to the next.

Wouldn’t it be great if the built-in gradient tool in QGIS could correct for lightness? Too bad the current dialog is not that great:

My first reaction therefore was to write a short script to import gradients from Gregor’s Chroma.js Color Scale Helper into QGIS:

But we’ll probably have a much better solution in QGIS soon since Nyall Dawson has picked up the idea and is already working on a completely new version of the gradient tool. You can see a demo of the current work in progress here:

I’m really looking forward to trying this out once it hits master!


How to fix the Windows config for .qgs default program

This is a short tip for you if you use QGIS on Windows and ended up with an error like this:

The program can't start because qgis_app.dll is missing from your computer. Try reinstalling the program to fix the problem.

Windows’ suggestion to reinstall probably won’t fix this issue. Instead, you want Windows to run qgis.bat instead of any .exe it is trying to use. Right-click a .qgs file and go to Open with | Choose default program:

Screenshot 2016-03-26 16.22.15

In OSGeo4W, the .bat file is located in the bin folder:

Screenshot 2016-03-26 16.27.01

Happy QGISing!


Creating dynamic icon series

Today’s post was motivated by a question on GIS.StackExchange, which is looking for an automated way to symbolize the amenities available at a location using a series of icons, like this:

Screenshot 2016-03-19 23.02.30

Assuming the information is available in  a format similar to this example attribute table

Screenshot 2016-03-19 23.02.00

we can create a symbol, which adapts to the values in the icon columns using data-defined overrides:

Screenshot 2016-03-19 23.04.17

The five potential symbol locations are aligned next to each other using offsets. We use the following expression to determine the correct SVG symbol:

CASE
WHEN "icon4" = 'dinner'
 THEN 'C:/OSGeo4W64/apps/qgis-dev/svg/entertainment/amenity=restaurant.svg'
WHEN "icon4" = 'sleep'
 THEN 'C:/OSGeo4W64/apps/qgis-dev/svg/accommodation/accommodation_hotel2.svg'
WHEN "icon4" = 'ship'
 THEN 'C:/OSGeo4W64/apps/qgis-dev/svg/transport/amenity=ferry_terminal.svg'
WHEN "icon4" = 'house'
 THEN 'C:/OSGeo4W64/apps/qgis-dev/svg/accommodation/accommodation_house.svg'
 ELSE  ''
END

To hide icons if the icon value is NULL, the marker size is set to 0 using, for example:

CASE
WHEN "icon4" is not NULL
 THEN 4
 ELSE 0
END

Finally, to ensure that the labels don’t cover the icons, we can use the cartographic label placement with the position priority set to ‘TR,TL,BL’, which restricts labels to the top right, top left, and bottom left position.

Screenshot 2016-03-19 23.04.43

With these settings in place, we can zoom out and the labeling algorithm picks the most suitable position from the list of allowed positions:

Screenshot 2016-03-19 23.02.11

For more cartography tips and tricks check my new book QGIS Map Design or join my QGIS training courses.


How to create a graduated renderer for polygon borders instead of fills

Today’s post was motivated by a recent question on the #gistribe Twitter chat:

So what’s the issue?

Default polygon symbols come with a fill and a border color:

Screenshot 2016-03-12 15.40.37

When they are used in a graduated renderer, the fill color is altered for each class:

Screenshot 2016-03-12 15.40.26

What if you want to change the border color instead?

The simplest solution is to add an outline symbol layer to your polygon symbol:

Screenshot 2016-03-12 15.40.46

The outline layer has only one color property and it will be altered by the graduated renderer.

If you now hit ok, the graduated renderer will alter both the simple fill’s fill color and the outline’s color. To stop the fill color from changing, select the simple fill and lock it using the small lock icon below the list of symbol layers:

Screenshot 2016-03-12 15.40.50

Voilà:

Screenshot 2016-03-12 15.40.58

For more cartography tips and tricks check my new book QGIS Map Design or join my QGIS training courses.


Better digitizing with QGIS 2.14

Tracing button

If you are using QGIS for digitizing work, you have probably seen the 2.14 Changelog entry for Trace Digitizing. The main reason why this is a really cool new feature is that it speeds up digitizing a lot. When tracing is enabled, the digitizing tools take care to follow existing features (as configured in the snapping options). For a detailed howto and videos check Lutra’s blog.


QGIS Map Design is out now!

My latest book “QGIS Map Design”, co-authored with well-known cartography expert Gretchen Peterson and with a foreword by the founder of QGIS, Gary Sherman himself, is now available as e-book.

In three parts, the book covers layer styling, labeling, and designing print maps. All recipes come with data and project files so you can reproduce the maps yourself.

Check the book website for the table of contents and a sample chapter.

Just in time for the big QGIS 2.14 LTR release, the paperback will be available March 1st.

On a related note, I am also currently reviewing the latest proofs of the 3rd edition of “Learning QGIS”, which will be updated to QGIS 2.14 as well.

Happy QGISing!


Experiments in the 3rd dimension

The upcoming 2.14 release of QGIS features a new renderer. For the first time in QGIS history, it will be possible to render 2.5D objects directly in the map window. This feature is the result of a successful crowd funding campaign organized by Matthias Kuhn last year.

In this post, I’ll showcase this new renderer and compare the achievable results to output from the Qgis2threejs plugin.

For this post, I’m using building parts data from the city of Vienna, which is publicly available through their data viewer:

This dataset is a pretty detailed building model, where each building is made up of multiple features that represent parts of the building with different height. Of course, if we just load the dataset in default style, we cannot really appreciate the data:

Loaded building parts layer

Loaded building parts layer

All this changes if we use the new 2.5D renderer. With just a few basic settings, we can create 2.5D representations of the building parts:

QGIS 2.5D renderer settings

QGIS 2.5D renderer settings

Compare the results to aerial images in Google Maps …

QGIS 2.5D renderer and view in Google Maps

QGIS 2.5D renderer and view in Google Maps

… not bad at all!

Except for a few glitches concerning the small towers at the corners of the building, and some situations where it seems like the wrong building part is drawn in the front, the 2.5D look is quite impressive.

Now, how does this compare to Qgis2threejs, one of the popular plugins which uses web technologies to render 3D content?

One obvious disadvantage of Qgis2threejs is that we cannot define a dedicated roof color. Thus the whole block is drawn in the same color.

On the other hand, Qgis2threejs does not suffer from the rendering order issues that we observe in the QGIS 2.5D renderer and the small towers in the building corners are correctly displayed as well:

QGIS 2.5D renderer and QGIS2threejs output

QGIS 2.5D renderer and Qgis2threejs output

Overall, the 2.5D renderer is a really fun and exciting new feature. Besides the obvious building usecase, I’m sure we will see a lot of thematic maps making use of this as well.

Give it a try!

In the next post, I’m planning a more in-depth look into how the 2.5D renderer works. Here’s a small teaser of what’s possible if you are not afraid to get your hands dirty:


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