If you want more control over the attributes of the merged feature than the
Dissolve tool allows, use the
Merge Selected Features tool in the Advanced Digitizing toolbar.
Manually select the features you want to merge into one feature. Click the
Merge Selected Features button. Now you get a popup window, that allows you to set the attributes of the merged feature. For every attribute table field, you can choose from these options:
- Feature 1/2/3 etc (take the attribute from one feature, and discard the others)
- mathematical calculations for numerical fields: Count, Sum, Mean, Median, Standard deviation (pop or sample), Minimum, Maximum, Range, Minority, Majority, Variety, Q1, Q3, IQR
- concatenation for text fields
- Skip attribute (replace with NULL)
- Manual value (type whatever you want)
Obviously the downside of this tool is that you have to do each set of features separately, so it can be time-consuming if you have a lot of features. You can achieve a similar level of control over the attributes by first Dissolving, then running
join attributes by location (summary).