I am trying to get the Extract by Location algorithm to work in the process modeler but I can not figure out which algorithms to include in the parent algorithm in order to get it to work.

I've been able to get it to work in the past but going through every combination with 6 different algorithms (64?) is extremely time consuming and isn't working.

The purpose of the model is to extract changes in road network by comparing historical data with new data. It builds a buffer around the new data and checks to see if the historical data falls outside of the buffer. Any changes are extracted to be used for field research. The interstate buffer is used to remove any motorway_links that are not on or near an interstate.

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    For the new data, is it necessary to reproject the layer twice? Can you also please edit your question to describe what your model does and why all the outputs of the algorithms are being fed into the final Extract by location tool? :) – Joseph Nov 10 '17 at 10:46
  • @Joseph I've updated the question and added a revised model. I got this to work through trial and error but I would like to understand how extract by location parent algorithms work because I will most likely have to edit this model in the future. The reason for the 2nd reproject is because dissolve polygons outputs the data in it's own projection (100002) not related to the project or the input data. – brink Nov 14 '17 at 17:29
  • The parent algorithm means that your chosen tool (in your case Extract by location) will only run once it receives the required outputs. So for the final Extract by Location tool, if you chose the two inputs as parent algorithms then it will run when the rest of the model has finished. – Joseph Nov 15 '17 at 10:27

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