This might be a very simple thing, but I just can't figure it out how to do it in QGIS (alternatively I'm also grateful for explanations for ArcGIS). I have a fisheries dataset with multiple catches in one location. I'd like to display these catches as a dot varying in size according to the number of catches - like dots displaying population size in a city. However, the excel sheet I have is one catch each row, with the same coordinates but different attributes (length, weight, etc). Is there a tool in QGIS that can merge all points in one location (other attributes not needed then)? Thanks a lot for your help!
I don't know which version of QGIS you have, but you should have the OSGeo4W desktop icon. So the simplest way to accomplish your task consists into double click on this icon, navigate to the folder containing your data (e.g.
catches.shp) and then type:
ogr2ogr catches_merge.shp catches.shp -dialect sqlite -sql "SELECT *, COUNT(geometry) AS NUM_CATCH FROM catches GROUP BY geometry"
The result, i.e.
catches_merge.shp, should be what you're looking for. See the OGR SQL page for more details.