QGIS styling options have advanced a lot in the last releases. But there’s always something more we would love to have … Greedy users!

Inkscape and other graphics programs can do it: Gradient fills.

Inspired by a question on gis.stackexchange, I tried to create something as close to a gradient fill as possible.

What I came up with is a symbol consisting out of multiple stacked “simple line” layers. The top-most layer is the dark outer border and every following layer is getting lighter and growing towards the center of the polygon (using a positive offset value). Important options are flat cap styles for all line layers and – of course – enabled symbol levels.

A "gradient" fill in QGIS

As you can see, the gradient looks quite fine inside the polygons. For the edges, it would be necessary to add a mask hiding the unclean rendering. Or maybe there is another solution which I just couldn’t think of?

Nicer map using a mask

This is the symbol source if you want to try it. Paste it into your symbology-ng-style.xml document.

    <symbol outputUnit="MM" alpha="1" type="fill" name="gradient">
      <layer pass="0" class="SimpleFill" locked="0">
        <prop k="color" v="255,255,255,255"/>
        <prop k="color_border" v="0,0,0,255"/>
        <prop k="offset" v="0,0"/>
        <prop k="style" v="solid"/>
        <prop k="style_border" v="solid"/>
        <prop k="width_border" v="1"/>
      </layer>
      <layer pass="0" class="SimpleLine" locked="0">
        <prop k="capstyle" v="flat"/>
        <prop k="color" v="240,240,240,255"/>
        <prop k="customdash" v="5;2"/>
        <prop k="joinstyle" v="bevel"/>
        <prop k="offset" v="6"/>
        <prop k="penstyle" v="solid"/>
        <prop k="use_custom_dash" v="0"/>
        <prop k="width" v="6"/>
      </layer>
      <layer pass="0" class="SimpleLine" locked="0">
        <prop k="capstyle" v="flat"/>
        <prop k="color" v="220,220,220,255"/>
        <prop k="customdash" v="5;2"/>
        <prop k="joinstyle" v="bevel"/>
        <prop k="offset" v="5.5"/>
        <prop k="penstyle" v="solid"/>
        <prop k="use_custom_dash" v="0"/>
        <prop k="width" v="5.5"/>
      </layer>
      <layer pass="0" class="SimpleLine" locked="0">
        <prop k="capstyle" v="flat"/>
        <prop k="color" v="200,200,200,255"/>
        <prop k="customdash" v="5;2"/>
        <prop k="joinstyle" v="bevel"/>
        <prop k="offset" v="5"/>
        <prop k="penstyle" v="solid"/>
        <prop k="use_custom_dash" v="0"/>
        <prop k="width" v="5"/>
      </layer>
      <layer pass="0" class="SimpleLine" locked="0">
        <prop k="capstyle" v="flat"/>
        <prop k="color" v="180,180,180,255"/>
        <prop k="customdash" v="5;2"/>
        <prop k="joinstyle" v="bevel"/>
        <prop k="offset" v="4.5"/>
        <prop k="penstyle" v="solid"/>
        <prop k="use_custom_dash" v="0"/>
        <prop k="width" v="4.5"/>
      </layer>
      <layer pass="0" class="SimpleLine" locked="0">
        <prop k="capstyle" v="flat"/>
        <prop k="color" v="160,160,160,255"/>
        <prop k="customdash" v="5;2"/>
        <prop k="joinstyle" v="bevel"/>
        <prop k="offset" v="4"/>
        <prop k="penstyle" v="solid"/>
        <prop k="use_custom_dash" v="0"/>
        <prop k="width" v="4"/>
      </layer>
      <layer pass="0" class="SimpleLine" locked="0">
        <prop k="capstyle" v="flat"/>
        <prop k="color" v="140,140,140,255"/>
        <prop k="customdash" v="5;2"/>
        <prop k="joinstyle" v="bevel"/>
        <prop k="offset" v="3.5"/>
        <prop k="penstyle" v="solid"/>
        <prop k="use_custom_dash" v="0"/>
        <prop k="width" v="3.5"/>
      </layer>
      <layer pass="0" class="SimpleLine" locked="0">
        <prop k="capstyle" v="flat"/>
        <prop k="color" v="120,120,120,255"/>
        <prop k="customdash" v="5;2"/>
        <prop k="joinstyle" v="bevel"/>
        <prop k="offset" v="3"/>
        <prop k="penstyle" v="solid"/>
        <prop k="use_custom_dash" v="0"/>
        <prop k="width" v="3"/>
      </layer>
      <layer pass="0" class="SimpleLine" locked="0">
        <prop k="capstyle" v="flat"/>
        <prop k="color" v="100,100,100,255"/>
        <prop k="customdash" v="5;2"/>
        <prop k="joinstyle" v="bevel"/>
        <prop k="offset" v="2.5"/>
        <prop k="penstyle" v="solid"/>
        <prop k="use_custom_dash" v="0"/>
        <prop k="width" v="2.5"/>
      </layer>
      <layer pass="0" class="SimpleLine" locked="0">
        <prop k="capstyle" v="flat"/>
        <prop k="color" v="80,80,80,255"/>
        <prop k="customdash" v="5;2"/>
        <prop k="joinstyle" v="bevel"/>
        <prop k="offset" v="2"/>
        <prop k="penstyle" v="solid"/>
        <prop k="use_custom_dash" v="0"/>
        <prop k="width" v="2"/>
      </layer>
      <layer pass="1" class="SimpleLine" locked="0">
        <prop k="capstyle" v="flat"/>
        <prop k="color" v="60,60,60,255"/>
        <prop k="customdash" v="5;2"/>
        <prop k="joinstyle" v="bevel"/>
        <prop k="offset" v="1.5"/>
        <prop k="penstyle" v="solid"/>
        <prop k="use_custom_dash" v="0"/>
        <prop k="width" v="1.5"/>
      </layer>
      <layer pass="2" class="SimpleLine" locked="0">
        <prop k="capstyle" v="flat"/>
        <prop k="color" v="40,40,40,255"/>
        <prop k="customdash" v="5;2"/>
        <prop k="joinstyle" v="bevel"/>
        <prop k="offset" v="1"/>
        <prop k="penstyle" v="solid"/>
        <prop k="use_custom_dash" v="0"/>
        <prop k="width" v="1"/>
      </layer>
      <layer pass="3" class="SimpleLine" locked="0">
        <prop k="capstyle" v="flat"/>
        <prop k="color" v="20,20,20,255"/>
        <prop k="customdash" v="5;2"/>
        <prop k="joinstyle" v="bevel"/>
        <prop k="offset" v="0.5"/>
        <prop k="penstyle" v="solid"/>
        <prop k="use_custom_dash" v="0"/>
        <prop k="width" v="1"/>
      </layer>
      <layer pass="4" class="SimpleLine" locked="0">
        <prop k="capstyle" v="flat"/>
        <prop k="color" v="10,10,10,255"/>
        <prop k="customdash" v="5;2"/>
        <prop k="joinstyle" v="bevel"/>
        <prop k="offset" v="0"/>
        <prop k="penstyle" v="solid"/>
        <prop k="use_custom_dash" v="0"/>
        <prop k="width" v="0.5"/>
      </layer>
    </symbol>

Infrastructure Coverage based on Open Data

By underdark

2011-07-24

GRASS, OSM, PostGIS

18 Comments

This is something I have been wanting to do for a long time: map which areas of Vienna have fast access to a certain kind of infrastructure. Now, I finally found time and data to perform this analysis. Data used is OSM road data (Cloudmade shapefile) for Austria and metro station coordinates for Vienna by Max Kossatz and Robert Harm.

Before importing the OSM roads into PostGIS, I cut out my area of interest and created a clean topology using GRASS v.clean.break. Once loaded into the database, assign_vertex_id() function does the rest and the network is ready for routing and distance calculations.
For the metro stations, I calculated the nearest network node using George MacKerron’s Nearest Neighbor function.

Catchments were calculated using driving_distance() function. It returns distance to a given metro station for all network nodes (up to a maximum distance). The result can be interpolated to show e.g. which areas are at most 1 km away from any metro station.

1 km catchments around metro stations in Vienna

Close-up look at the 1 km catchment zone border

Once set up, performing this analysis is reasonably fast. Instead of metro stations, any other infrastructure coverage can be analyzed easily. I could imagine this being really useful when looking for a new flat: “Find me an area close to work, a metro station and a highschool.”

The next great thing would be to have all data for calculation of transit travel times too. Yes, I’m looking at you Wiener Linien!

QGIS Server on Windows

By underdark

2011-07-18

GIS, QGIS Server

Want to finally try QGIS Server on your Windows system? Thankfully, Till Adams has written a new HowTo for QGIS Server on Windows. Till shows how to install OSGeo4W version and how to get it running.

If you first want to see what QGIS Server and QGIS Webclient can do, check Webgis-Uster homepage by Andreas Neumann.

Finding Open Data – DataCatalogs.org

By underdark

2011-07-06

OpenGovermentData

DataCatalogs.org aims to be the most comprehensive list of open data catalogs in the world. […] The alpha version of DataCatalogs.org was launched at OKCon 2011 in Berlin.

As of today, 134 data catalogs have been registered. From Dalian, China to Rhode Island, data from all over the world is ready to be discovered.

Open data and open GIS – 2011 is an exciting year!

Open Government Data Wien in QGIS

By underdark

2011-06-30

GIS, OpenGovermentData, QGIS

Vienna’s Open Government Data initiative is publishing an increasing amount of Geodata and the best thing is: They’re publishing it via open standardized services! Both WMS and WFS are available and ready to be used in QGIS.

Let’s see how we can use the data available through their WFS using the district information layer “Bezirksgrenzen” as an example. The page lists a GML and a GeoJSON version of WFS. For now, we’ll use GeoJSON.

In QGIS, the layer can be loaded using “Add vector layer” – “Protocol” and inserting the GeoJSON url there. The encoding should be changed to ISO8859-15 to account for “Umlaute”.

The loaded GeoJSON layer "Bezirksgrenzen"

Now, we have geodata. Let’s add some attribute data too! Attribute data is available in CSV format. After downloading e.g. some information on the district population, check the file content and remove excessive header lines so that there is only one header line containing attribute names left. Then, you can load the CSV file into QGIS too (“Add vector layer”).

Last step: Joining geodata and attribute data! Go to the vector layer’s properties – Join tab and add the following join relation:

Joining GeoJSON and attribute layer

Now, the attribute table of the vector layer contains the additional CSV attributes – ready for further analysis. If you want to classify based on numerical CSV attributes, you’ll have to create a .csvt file first otherwise all fields are interpreted as texts.

Works great. Thumbs up for this great initiative!

QGIS 1.7 Released!

By underdark

2011-06-20

GIS, QGIS

2 Comments

QGIS 1.7 has landed. After some delays due to a major infrastructure overhaul, a new version of QGIS is available for download. For a list of what’s new in 1.7 check the release announcement.

Browsing Spatial Data with QGIS Browser

By underdark

2011-06-16

QGIS

12 Comments

QGIS trunk now comes with a separate tool called “QGIS Browser”. It enables the user to browse through all spatial data files on the system as well as all WMS configured in QGIS. Both files and WMS layers are listed in a tree widget on the left side while metadata, attributes and a preview can be seen on the right.

WMS preview in QGIS Browser

This is a great way for example to check through all layers of a WMS fast and without having to go through the “Add WMS Layer” dialog in QGIS all the time.

Multi-line Labels in QGIS

By underdark

2011-06-15

GIS, QGIS

10 Comments

Ever wondered how to create multi-line labels in QGIS? The new labeling engine has a “Multiline labels” option but it’s not so obvious how to create a usable labeling attribute. Here is how it works (credits to @nhopton on QGIS forum):

Create a big enough text field (if the data doesn’t contain any yet).
In Layer Properties – Fields, chose a “Text edit” edit widget for the label field.
Enter the multi-line text into the label field. You can do this using Attribute Table or Feature Form.
A feature form with "Text edit" widget
Activate labeling. You’ll have to tick “Multiline labels” option in Layer Labeling Settings – Advanced – Options. That’s it:
Simple multi-line label example

A common use case is the wish to show multiple attribute values in a feature’s label. Using Field Calculator, you can combine them into multi-line labels. All you need is to combine the fields with the || operator and add ‘\n’ (newline) wherever there should be a line break:

Field1 || '\n' || Field2

Populating a multi-line label field using Field Calculator

And finally, the result:

Multi-line labels displaying city name and population

WMS-T Support in Geoserver and Mapserver

By underdark

2011-06-10

GeoServer, GIS, Mapserver, spatio-temporal data

“-T”, this small appendix can be found after many popular GIS-related acronym. But of course, it always means something different. Take for example GIS-T (GIS for Transportation), WFS-T (Transactional WFS) and WMS-T (WMS with time support). The world of acronyms is a fun place!

Let’s see what a WMS-T can do for us. From the WMS standard:

Some geographic information may be available at multiple times (for example, an hourly weather map). A WMS
may announce available times in its service metadata, and the GetMap operation includes a parameter for
requesting a particular time. […] Depending on the context, time
values may appear as a single value, a list of values, or an interval, …

Currently, only Mapserver supports WMS-T but the Geoserver team is working on it.

Mapserver

MapServer 4.4 and above provides support to interpret the TIME parameter and transform the resulting values into appropriate requests.

Time attributes are specified within the metadata section:

METADATA "wms_title" "Earthquakes" "wms_timeextent" "2011-06-01/2011-07-01" "wms_timeitem" "TIME" "wms_timedefault" "2011-06-10 12:10:00" END

Mapserver supports temporal queries for single values, multiple values, single range values or even multiple range values:

...&TIME=2011-06-10&... ...&TIME=2011-06-10, 2004-10-13, 2011-06-19&... ...&TIME=2011-06-10/2011-06-13&... ...&TIME=2011-06-10/2011-06-15, 2011-06-20/2011-06-25&...

Geoserver

GeoSolutions has developed support for TIME and ELEVATION dimensions in WMS.
There are plans to backport this feature to the stable 2.1.x series after the 2.1.1 release.

Configuration of time-enabled layers can be done via the normal user interface:

The following video by GeoSolutions demonstrates the use of Geoserver’s WMS-T:

Both server solutions seem to support only one time attribute per layer. An optional second time attribute would be nice to support datasets with start and end time like Time Manager for QGIS does.

Free and Open Source GIS on gis.stackexchange.com

By underdark

2011-06-09

GIS

The gis.stackexchange community keeps on growing and it’s questions and answers span a wide spectrum of GIS-related topics. As of today, the page lists 2,700 questions and 6,400 answers.

As was to be expected, ‘arcgis’ (549 times) is the most used tag followed by ‘arcgis-10.0’ ;)

From an open source perspective, PostGIS gets most attention (rank 8), followed closely by OpenLayers (rank 9) and Geoserver (rank 10). QGIS is the highest-ranked desktop GIS (rank 13). Users of other open source desktop GIS like uDig or gvSIG don’t seem to be using this platform yet.

Here’s the full list of open source GIS tags with a count of more than 10:

postgis × 149
openlayers × 137
geoserver × 121
qgis × 97
open-source × 94
grass × 85
gdal × 68
postgresql × 32
pgrouting × 20
geodjango × 14
mapnik × 13