The Geodetic Equivalent map is useful for a variety of things e.g. looking at major transits that are impacting a particularly large area of the world, perhaps spotlighting the cause of a hurricane or earthquake. But what are geodetic equivalents?
While the idea was played around with by astrologers as far back as Ptolemy, pioneering work on the subject was published in a book around 1925 by the astrologer Sepharial (aka Walter Gorn). He suggested that if you take the prime meridian (the zero degree line that passes through Greenwich) and associate it with 0 degrees Aries on the MC of a chart, each succeeding sign placed likewise at 30 degree intervals (thus 30 degrees east = 0 Taurus, 60 degrees east = 0 Gemini, etc.), you have what he called “the Geodetic Equivalent of longitude.” This technique was expanded on, and written further about, by astrologer L. Edward Johndro.
Some people use it as an adjunct to help understand how various cultures sprang up in the world. For example, almost the entire continent of Australia has Leo for its Geodetic Equivalent MC. Perhaps this says a lot about the very ancient Indigenous cultures that developed there.
>> To apply the Geodetic Equivalents to an Astro Locality map
1.Open any chart (you can use a natal chart, the chart for an event, any chart you would like to ‘map’)
2.Click the globe icon 
in the toolbar to open the world map
3.In the "Astro Locality Mapping" window click the button on top of the map that says Lines. The "Chart Points" window will open.
4.At the top of the "Chart Points" window choose Zodiacal.
5.If you just want to see the Geodetic equivalent sign lines, you can untick the first four boxes (MC/Culminate, IC/AntiCulminate, Asc/Rise, Dsc/Set). However leave them ticked if you want to see the planetary lines.
6.Untick the Planetary Directions box.
7.Under "Celestial", tick all three (Ecliptic, Signs on MC, and Signs on Asc).
8.Under "Geographical" the Equator and Tropics boxes are optional.
9.Last, and most importantly, under "Zodiacal Offset" tick Geodetic (Mundane).
You will now see the Geodetic Equivalent MC (and Asc) lines.
And if you have any doubt that the planet lines are different in Geodetic than in the regular Locality map, untick the Geodetic (Mundane) box and watch them all change on the map.
