Hubway is a bike sharing system in Boston and they are currently hosting a data visualization challenge. What a great chance to play with some real-world data!

To get started, I loaded both station Shapefile and trip CSV into a new Spatialite database. The GUI is really helpful here – everything is done in a few clicks. Afterwards, I decided to look into which station combinations are most popular. The following SQL script creates my connections table:

create table connections (
start_station_id INTEGER,
end_station_id INTEGER,
count INTEGER,
Geometry GEOMETRY);


insert into connections select 
start_station_id, 
end_station_id, 
count(*) as count, 
LineFromText('LINESTRING('||X(a.Geometry)||' '||Y(a.Geometry)||','
                          ||X(b.Geometry)||' '||Y(b.Geometry)||')') as Geometry
 from trips, stations a, stations b
where start_station_id = a.ID 
and end_station_id = b.ID
and a.ID != b.ID
and a.ID is not NULL
and b.ID is not NULL
group by start_station_id, end_station_id;

(Note: This is for Spatialite 2.4, so there is no MakeLine() method. Use MakeLine if you are using 3.0.)

For a first impression, I decided to map popular connections with more than one hundred entries. Wider lines mean more entries. The points show the station locations and they are color coded by starting letter. (I’m not yet sure if they mean anything. They seem to form groups.)

Some of the stations don’t seem to have any strong connections at all. Others are rather busy. The city center and the dark blue axis pointing west seem most popular.

I’m really looking forward to what everyone else will be finding in this dataset.

Exploring Mobility Data Using Time Manager

By underdark

2012-09-11

QGIS, spatio-temporal data, Visualization

4 Comments

Data from various vehicles is collected for many purposes in cities worldwide. To get a feeling for just how much data is available, I created the following video using QGIS Time Manager which has been shown at the Austrian Museum of Applied Arts “MADE 4 YOU – Design for Change”. It shows one hour of taxi tracks in the city of Vienna:

If you like the video, please go to http://www.ertico.com/2012-its-video-competition-open-vote and vote for it in the category “Videos directed at the general public”.

3 Reasons to Move Your QGIS Plugins to the New Repository

By underdark

2012-09-05

QGIS

7 Comments

Since the release of QGIS 1.8, Plugin Installer no longer includes the “add 3rd party repositories” button. This was an intentional design choice!
The new official plugin repository at plugins.qgis.org keeps everything in one place making it easier for users to find documentation and report issues. It will also provide many long-wanted features such as a rating system for plugins. You can already sort by number of downloads to discover the most popular plugins.
Last but not least: New users will not be able to discover your plugin if it is not in the repository.

Go ahead to plugins.qgis.org and upload your plugin now!

Introducing the Latest Style User Interface Improvements

By underdark

2012-08-15

QGIS

4 Comments

Yesterday, Martin Dobias announced that Arun’s GSoC work on QGIS symbology has been merged into the developer version. So let’s have a look at todays nightly-build!

I’ll step through the features mentioned in the announcement to see how they look and work:

1. Style manager has been greatly improved: grouping of symbols, tagging, “smart” groups (showing only symbols matching some criteria), search

On opening new Style Manager, we can already see that it has changed considerably: There are groups on the left, tags at the bottom and a search field in the upper right corner.

new Style Manager

New groups are created with the “+” button and styles can be added using the context menu:

adding a style to a group

2. Symbol selector and properties dialogs have been integrated to just one dialog, improving the usability a lot

Instead of opening tons of nested windows, complex styles can now be easily edited using the symbol layer tree on the left:

3. Style database is now stored in a SQLite database rather than an XML file for better scalability. You can import all your saved symbols and color ramps from ~/.qgis/symbology-ng-style.xml – from now they will be stored in ~/.qgis/symbology-ng-style.db.

Importing through Style Manager works like a charm. All styles will be imported into the given group.

importing previous style.xml

4. Style import improvements: load style directly from given URL, saving imported symbols into a group

Instead of giving a path to a style XML, it’s also possible to specify a URL. That’s a great step towards shared symbol libraries!

5. SVG fill: shows directories for easier traversal through the SVG directories

Definitely a plus! It’s now much easier to work with big SVG symbol collections.

What a great result of this year’s Google Summer of Code for QGIS. Give these new features a try! I already fell in love with them.

Stamen Maps for QGIS

By underdark

2012-07-21

QGIS

24 Comments

Stamen’s maps are amongst the most creative and beautiful OpenStreetMap visualizations and it would be great to have them as base maps in QGIS.

No problem! Nathaniel Kelso has already done all the work for us and we can download the extended OpenLayers plugin from his Github page. (There is a pull request in place to add Stamen to the default plugin too.)

Simply unpack the plugin into QGIS’ plugin folder. As you can see in the following screen shot, I’ve put it besides the “original” OpenLayers 0.6.2 plugin. In QGIS plugin manager, I then switched to Nathaniel’s version.

It adds the possibility to load Stamen’s Watercolor, Toner and Terrain tiles into the QGIS project:

Like all other OpenLayers layers, these can now be overlaid with more data such as this heatmap which is based on Twitter data I presented in a previous post, processed using Heatmap plugin and semi-transparently overlaid onto Stamen’s Toner map:

Physical Maps on QGIS Cloud

By underdark

2012-06-27

Cartography, QGIS

8 Comments

QGIS Cloud is a great cloud hosting service for QGIS Server by Sourcepole. After online registration and installation of an (experimental) plugin, QGIS projects can be uploaded to the cloud quite comfortably.

For a quick test, I tried to recreate the map from “Open Data for Physical Maps”. Right now, one of the limitations is that raster layers cannot be uploaded. Instead of the SRTM data, I therefore chose OCM landscape from OpenLayers plugin to provide some hillshade. The process of uploading data and publishing the project went smoothly and I didn’t encounter any problems.

You can explore the map online at qgiscloud.com/anitagraser/corine_austria.

Considering the complexity of the Corine dataset, rendering is quite fast – certainly much better than on my notebook.

Open Data for Physical Maps

By underdark

2012-06-17

Cartography, QGIS

8 Comments

Corine Land Cover is a European program to create a land cover inventory of Europe. The data is freely available and a valuable input for many analyses. In this post, we’ll be using it to create a physical map.

For the background, reused the hillshade presented in “Mapping Open Data With Open GIS”

Instead of the standard grayscale, I defined a sand-colored colormap that looks warmer and more natural:

On top of this hillshade, I put the Corine land cover layer. Instead of the official, rather bright colors I selected a more neutral color palette and varying transparency values: Water areas are drawn with no transparency while forests are set to 50 % and built-up areas to up to 80 % transparency. I also skipped classes such as “bare rock” by setting them to be totally transparent:

On top of the land cover, I added a river dataset and styled it with the same color used for water surfaces in the Corine layer. Obviously, this is an optional step. Big rivers are visible within the land cover data too.

After adding a mask and labels, the map is ready to add the finishing touches in Print Composer: Title, explanatory text and a scale bar. I decided against adding a legend to this particular map since I hope that the color choices are intuitive enough.

If you want to create your own physical map, you can use Corine Land Cover for European regions or the National Vegetation Classification in the U.S.

A Rainbow Gradient for QGIS Vectors

By underdark

2012-06-15

QGIS

3 Comments

Here’s a rainbow gradient for use with QGIS “Categorized” or “Graduated” vector renderer:

<!DOCTYPE qgis_style>
<qgis_style version="0">
  <symbols/>
  <colorramps>
    <colorramp type="gradient" name="rainbow">
      <prop k="color1" v="250,8,8,255"/>
      <prop k="color2" v="92,11,122,255"/>
      <prop k="stops" v="0.3;237,244,25,255:0.5;46,155,45,255:0.66;29,18,122,255:0.82;152,6,130,255"/>
    </colorramp>
  </colorramps>
</qgis_style>

(Save as .xml and import using QGIS Style Manager.)

I’ll put it on my QGIS Resources Github repository too. Soon.

Mapping Open Data With Open GIS

By underdark

2012-06-07

Cartography, QGIS

16 Comments

This post explores some cartographic features of QGIS while mapping the river network of Tirol, Austria. All data used is freely available.

For the background, I downloaded NASA SRTM elevation data from CGIAR-CSI and created a hillshade using Terrain Analysis tools in QGIS 1.8.

To emphasize both state borders and the fact that Tirol consists of two separate areas, I created a mask using the Difference tool and styled it a transparent white.

The river network is too dense to label all rivers on an A4 map. Expression-based labels make it possible to only label selected features. For this dataset, the expression limits labeling to features with certain values of GEW_WRRL attribute:

CASE WHEN (GEW_WRRL = '10.000 km2 Fluss' OR "GEW_WRRL"= '4.000 km2 Fluss' OR "GEW_WRRL"='1.000 km2 Fluss') AND length("GEW_NAME_A") < 10 THEN "GEW_NAME_A" END

Labels of neighboring areas together with map title, descriptions and scale bar were added in Print Composer.

Working with Print Composer, it is useful to know that you can use Copy&Paste to duplicate map components and right-click to lock them from being moved. Also, every new component by default comes with a black outline and white background which can (and should) be disabled/changed in “General options”.

This is the final QGIS Print Composer output – without any further post-processing in Inkscape or Gimp:

SLD Support and other QGIS 1.8 Style Features

By underdark

2012-06-03

QGIS

12 Comments

The upcoming 1.8 release contains many new features for handling layer styles.

Copy-paste Styles

Very handy new entries in the layer list context menu: “Copy Style” and “Paste Style” make copying layer styles really fast. You don’t even have to open layer properties anymore.

SLD Support

Besides the classic QML layer style files, QGIS 1.8 supports the SLD standard. SLDs can be exported from and imported into new symbology.

One thing worth to note: SLDs can be exported from any type of renderer: single symbol, categorized, graduated or rule-based, but when importing an SLD, either a single symbol or rule-based renderer is created.

That means that categorized or graduated styles are converted to rule-based. If you want to preserve those renderers, you have to stick to the QML format. On the other hand, it could be very handy sometimes to have this easy way of converting styles to rule-based.

Symbol Levels

If you are looking for the “Symbol level” settings, they have been moved to the “Advanced” button:

Rule-based Renderer

The rule-based renderer GUI got a major face-lift. Just compare the 1.7 version

Rule-based renderer GUI in 1.7

to the new clean 1.8 version:

Rule-based renderer in 1.8

Grouping of styles has been overhauled too: Using drag-and-drop, layers can be arranged into groups in a more flexible manner than previously possible.

There is also a new context menu which enables workflows such as changing the transparency of multiple symbols at once:

Symbol levels for the rule-based renderer can now be accessed via “Rendering order”.

It’s obvious that a lot of work has been put into style handling since the 1.7 release and these improvements are just a small fraction of what’s been done to get closer to the big goal: releasing 2.0.