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Using local tree data in open source software

by Anson Parker on 2019-12-05T16:28:00-05:00 | Comments

In this series we're going to be looking at using tree data for public health analysis.  The goal is present a series of methods for processing, analyzing, and curating public health data using trees as the population, and various insults such as blights, pestilence, etc... as the diseases. 

This methodology alleviates the need to address HIPAA concerns and allows us to create a public repository of data and methods for hands-on training.

For our initial repository we're pulling from trees from https://opendata.charlottesville.org/datasets/tree-inventory-point and the structure data available here https://opendata.charlottesville.org/datasets/existing-structure-area

Quick look at data in QGIS 

get geojson in opendata

First get the data - here's a link to the GEOJSON 

https://opendata.arcgis.com/datasets/e7c856379492408e9543a25d684b8311_79.geojson

import it in to qgis - click on the first icon on the top left - select protocol https: and then set the type to GEOJSON and paste the link in there

trees loading in to qgis

 

First we need to filter the content to "Ash" trees

 filtering content

"Common_Name" LIKE '%Ash%' is the filter to use - currently should return 109 values

Testing proximity is done with the "Vector->geoprocessing tools -> buffer" tool - 

.00005 degrees is roughly 5 meters - and then we'll also test .0001 for 10 meters

the image should look like this and there should be a layer called "buffer" available in the left side layer menu

buffer layer in qgis

now to see what trees are within 5m of a building go to "Vector->Research Tools->Select by Location"

intersecting property and trees

uh-oh!  there were errors in the geometries!  to ignore that and move on follow the instructions here https://gis.stackexchange.com/questions/289056/ignoring-invalid-input-features-with-intersection-tool-in-qgis and 

Once that's done you should see some items on the screen highlight to bright yellow 

Next right click on the buffered layer and save the selected points!

This will create the new layer that has all of the relevant data

 

 


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