I'm new to QGIS.
I'm trying to solve the following problem, using the tutorial here: http://www.qgistutorials.com/en/docs/performing_spatial_joins.html but haven't had any luck.
I have a QGIS file with two forms of spatial area data: Chicago's 77 community area boundaries on one layer, and the city's park system on another layer. The acreage of each park on the parks layer is in the ACRES column of the attribute table. What I would like to do, is find out what the total parkland acreage is within each of the 77 community areas. So if a community boundary line divides a park in half, it would obviously need to have half of its area contribute to the figure for community A and half of its area contribute for the parkland acreage in community B.
I have tried using Vector > Data Management Tools > Join attributes by location, with various options ticked and unticked, but every time it produces a new layer with a useless, blank attribute table. Then I thought perhaps this was the wrong way to go about it, so I did some more Googling and tried Vector > Geoprocessing Tools > Intersection, but this also produced a blank layer.
For your reference, I've zipped my folder containing the working file (10-mapping.qgs) and the layer files in a subfolder. Also included a screenshot of the two layers, Parks_Aug2012 and Community areas, turned on. Google drive link: https://drive.google.com/file/d/0B_uEI02m4m1OLUdnTTh3blR2OWM
I'm using QGIS 2.18.3