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To add to the excellent answer of @Spacedman (create a visited column as boolean (true/false) in your dataset):

If you wanted you could also create an integer (whole number) field named "times visited" or a date field named "last visit" on your layer and then create an appropriate symbology. I generally find it best to store the most detailed information in case I want to do more detailed analysis later. Maybe sometime in the future you want to create a map of the airports you last visited in 1999? Or the airports colored by year of last visit? Or all airports you visited in the last 5 years as red dots and all others as gray dots?

If you really want detailed data then create one entry per visit (instead of one per airport) and log detailed information per visit - anything you may want to visualize: weather conditions, time of day, airplane you used, co-pilots, ...).

To add to the excellent answer of @Spacedman (create a visited column as boolean (true/false) in your dataset):

If you wanted you could also create an integer (whole number) field named "times visited" or a date field named "last visit" on your layer and then create an appropriate symbology. I generally find it best to store the most detailed information in case I want to do more detailed analysis later. Maybe sometime in the future you want to create a map of the airports you last visited in 1999? Or the airports colored by year of last visit? Or all airports you visited in the last 5 years as red dots and all others as gray dots?

If you really want detailed data then create one entry per visit (instead of one per airport) and log detailed information per visit - anything you may want to visualize: weather conditions, time of day, airplane you used, co-pilots, ...).

You can not edit CSV layers directly in QGIS, so you need to save your CSV to a different format (Shapefile or SpatiaLite) and then add the fields there. To do so, right click the layer in the layer tree, choose "export".

To add to the excellent answer of @Spacedman (create a visited column as boolean (true/false) in your dataset):

If you wanted you could also create an integer (whole number) layer named "times visited" or a date layer named "last visit" and then create an appropriate symbology. I generally find it best to store the most detailed information in case I want to do more detailed analysis later. Maybe sometime in the future you want to create a map of the airports you last visited in 1999? Or the airports colored by year of last visit? Or all airports you visited in the last 5 years as red dots and all others as gray dots?

If you really want detailed data then create one entry per visit (instead of one per airport) and log detailed information per visit - anything you may want to visualize: weather conditions, time of day, airplane you used, co-pilots, ...).

To add to the excellent answer of @Spacedman (create a visited column as boolean (true/false) in your dataset):

If you wanted you could also create an integer (whole number) field named "times visited" or a date field named "last visit" on your layer and then create an appropriate symbology. I generally find it best to store the most detailed information in case I want to do more detailed analysis later. Maybe sometime in the future you want to create a map of the airports you last visited in 1999? Or the airports colored by year of last visit? Or all airports you visited in the last 5 years as red dots and all others as gray dots?

If you really want detailed data then create one entry per visit (instead of one per airport) and log detailed information per visit - anything you may want to visualize: weather conditions, time of day, airplane you used, co-pilots, ...).

To add to the excellent answer of @Spacedman (create a visited column as boolean (true/false) in your dataset):

If you wanted you could also create an integer (whole number) layer named "times visited" or a date layer named "last visit" and then create an appropriate symbology. I generally find it best to store the most detailed information in case I want to do more detailed analysis later. Maybe sometime in the future you want to create a map of the airports you last visited in 1999? Or the airports colored by year of last visit? Or all airports you visited in the last 5 years as red dots and all others as gray dots?

If you really want detailed data the create one entry per visit (instead of one per airport) and log detailed information per visit - anything you may want to visualize: weather conditions, time of day, airplane you used, co-pilots, ...).

To add to the excellent answer of @Spacedman (create a visited column as boolean (true/false) in your dataset):

If you wanted you could also create an integer (whole number) layer named "times visited" or a date layer named "last visit" and then create an appropriate symbology. I generally find it best to store the most detailed information in case I want to do more detailed analysis later. Maybe sometime in the future you want to create a map of the airports you last visited in 1999? Or the airports colored by year of last visit? Or all airports you visited in the last 5 years as red dots and all others as gray dots?

If you really want detailed data then create one entry per visit (instead of one per airport) and log detailed information per visit - anything you may want to visualize: weather conditions, time of day, airplane you used, co-pilots, ...).