Delete specific values for contour lines in an attribute table for deletion in line data with QGIS

Question

Issue:

I have an attribute table showing contour lines for both bathymetric and terrestrial data. As my study is entirely focused on the marine environment, I would only like my maps to show the bathymetric contour lines. The ' Interval between Contour lines' has been set to 500 m. My contour file is in line data format.

The attribute table has 6001 rows and I want to delete all the positive values to erase all the terrestrial contours, and for the bathymetric data, I want to delete -500m, -1500m, -2500m etc because the map looks chaotic.

Are there any time-saving techniques where I can filter the contour line values (en masse) within the attribute table and delete a large number of rows at the same time for the filtered values without deleting the entire column by accident?

Answer 1

1. (Open attribute table) Select them by expression,
2. start editing,
3. Delete, which will delete only the selected,
4. save edits,
5. stop editing