February '16 Meetup Minutes

Covered Topics:

• Openstreetmap Seattle
• Printing a map series
• Raster Image Classification and Analysis
• Publishing to Web Maps

Clifford Snow shared what the OpenStreetMap Seattle is up to. Check out their meetup.com page.

John Murphy is showed how to print out a series of paper maps.

• Used the OSM base map.
• Created a subdivision point feature layer from polygon building lot features using PostGIS database commands.
• Open a New Print Composer window from the Project menu.
  • Go to the Atlas Generation tab in the Atlas settings.
    • Set the coverage layer to subdivisions layer.
  • Add Map from the Layout menu.
    • In the Item properties for the Map, check Controlled by atlas. This will center an atlas page on each point feature in the subdivisions layer.
    • You can set it to zoom to each feature with a buffer. This was not adequate for especially small subdivisions.
  • Add Label from the Layout menu.
    • Labels can be a formula tied to layer attributes.
    • When writing the query for the labels. The “Insert expression” dialog shows the just query. The box on the Item properties tab has [% %] around the query which is necessary.
  • Select Preview Atlas from Atlas menu.
  • Use arrows in the tool bar to page through the atlas pages.
• John is trying to figure out how to hide the subdivisions that are not the current subject of an atlas page.

Bob Catherman - Part 2 Using QGIS to Process Raster Images.

• Using the NDVI calculation on Landsat image data.
• Between 2002 and 2014 there was a lot of development in the center of the study area.
• Vegetation increased in the previously developed lots, where landscaping grew in.
• Bob subtracted the 2014 NVDI from 2002 NDVI and applied a color ramp to show the change over time.
  • Bob created three categories: Loss of Vegetation; Gain of vegetation; and Neutral gain/loss.
• Final analysis result is very similar to the University of Maryland outcome. Differences can be attributed to:
  • Start and end points that were 1-2 years off from UMD.
  • UMD had a more clear definition of “forest” and had additional tree height data.
• Bobs slides are available on our Resources page.

Bob Catherman - SCP (Semi Automatic Classification Plugin)

• Using RGB Landsat 8 image.
• Bob selected an area he was familiar with in central Washington.
• When picking training areas, stay away from land cover edges.
• Bob created training areas with the following known land use:
  • Cemetery
  • Urban area
  • Plowed field
  • Water
• The result was pretty reasonable using only a few training areas, fewer than are recommended.
• The author of SCP issues updates often.
• Satellite data can be downloaded directly from the plugin.
• Bobs slides are available on our Resources page.

Bob Catherman has received feed back on his "Monitoring Health Care Outcomes Using GIS" handbook, which is available on our Resources page. Bob will be working on a raster hand book as well.

Paul McCombs gave a brief demonstration of the PSQGIS web site.

Stu Smith: Free and open web mapping resources available to QGIS

• qgis2web plugin
  • Creates a web map available on the internet.
  • Installs under web menu in QGIS.
  • Points are styled in QGIS as stars but they render as circles on the web map.
  • Stu’s example showed 2015 fire data near Lake Chelan.
  • Stu acquired boundaries of the Lake Chelan Fire Complex from the US Forest Service.
    • Stu will provide the URL on request.
    • It is available as a GeoPackage (*.gpkg)
    • Stu located three look out towers and generated point data using lat/lon coordinates.
    • Stu computed view sheds from the towers and elevation in ArcINFO years ago.
    • Stu used the OSM base map.
  • From the plugin, select an output folder that can be copied to any web server you have access to publish on.
  • Stu used the OpenLayers3 option because the Leaflet option resulted in an error.
• CartoDB plugin
  • Need to have a CartoDB account. Clifford Snow says it’s free.

On the agenda for next month:

• Stu will talk about GeoPackages.
• Evan Derickson will talk about QGIS cartography including hill shades, coastal vignettes and things you can’t do in ArcMap.