Thank you for comments.
Great Circles are of course here as said before. I suppose this was originaly started with these in mind. These can be tough to find.
Another Latitude locations are those markers that are on equal degree (like N/S 45 degrees etc.) .Basicly those that are mentioned here .
About those border crossings. Lot of border crossings just happens to been drawn in exact degree of latitude. Some of those border areas may have a markers that say that this border is forexample in 49 degree, between British Columbia and Washington.
Equal degree of Longitude markers can be waymarked also, Exept Prime meridian that is waymarked already in its own category.
Now I'm thinking that Time zones are better to leave out of this category. In most cases these are not straight lines as they follow national borders. Time zones are also mentioned in many places other than borders like in airport, harbours etc. These cases they don't have anything to do with equal longitudes or latitudes either.
Right name of the category would be Lines of Earth.
With markers that are waymarked. Give the distance to real longitude or latitude that this or that marker presents. (how far north/ south or east/ west is marker right latitude and longitude)
How about including old historical meridians : Paris meridian and even more rare antwerp meridian? There are markers of these also.
Some variable ideas.
Line type:
Great Circles (arctic,
Equal Latitudes
Equal Longitudes
Time zone *
Historical (Paris, Antwerp)
Marker type: Check box
Historical
Comercial (location is comercial and offers tourists other than historical data)
Artistical
Other
If other type. Please explain