[GIS] Displaying only points within polygon I created in QGIS

Question

I am trying to map policing activity in NYC for two areas: one area in the Bronx and another in Manhattan.

I want to display ALL of the activity but only WITHIN a couple of square blocks that I am interested in (not the whole precinct – which I have a shapefile for with boundaries already set). My assumption, is that I create a polygon outlining the block areas I want.

But then, how do I attach those boundary coordinates to my CSV database on police activity (that dataset has x y coordinates representing police activity)?

And then, how do I only display the activity within the boundaries rather than all of the activity that exists throughout NYC?

Answer 1

The majority of your problems can be solved with a basic GIS understanding. Therefore i advise you to read some tutorials on the net (for example here on GIS-tutor or click yourself through the QGis Wiki).

Regarding your way of proceeding:

• Load in your point data ( the one with x-y coordinates) as text-delimited file (search for advice on this site or in the tutorials)
• Create your polygons and make a simple spatial join with your points. Alternatively make a subset of your policing activity points to get only those points, which intersect or are contained by your polygons (blocks). You could also create a grid or make a simple join with your data if you stick to the same IDs and names. This entirely depends on what you want to achieve and how you want to display it.