Casting Qi Men Charts in the US & Canada: How to Enter a Western Longitude

Why Western Longitudes Are Negative

Charting tools follow the international convention: east is positive, west is negative. Beijing at 116.4°E is entered as 116.4; New York at 74°W must be entered as -74.

Getting the sign wrong is not a small error: entering New York as +74° (which is 74°E, near Pakistan) shifts the True Solar Time by about ten hours — the double-hour and even the day pillar all derail, and the resulting chart has nothing to do with you.

How to Find Your Longitude

Three ways, fastest first:

1. The tool’s GPS button: in the Qimena charting form, tap “Auto GPS” — after the browser permission prompt, the signed longitude is filled in automatically. This is the most error-proof way;
2. City presets: New York, Los Angeles, London, Sydney and other overseas cities are built into the dropdown;
3. Google Maps: long-press your location on the map; the second number in the popup coordinates is your longitude (shown as negative in the Americas — copy it as-is).

North American Longitude Quick Reference

City	Longitude	City	Longitude
New York	−74.01	Vancouver	−123.12
Los Angeles	−118.24	Toronto	−79.38
San Francisco	−122.42	Montreal	−73.57
Seattle	−122.33	Calgary	−114.07
Chicago	−87.63	Houston	−95.37
Boston	−71.06	Dallas	−96.80

What the Tool Does With Your Longitude

Anchored to your device’s time zone, the engine applies two corrections automatically (see True Solar Time explained):

1. Longitude offset: the gap between your actual longitude and your time zone’s reference meridian, at 4 minutes per degree;
2. Equation of Time: the seasonal orbital deviation (−14 to +16 minutes).

For example, in San Francisco (−122.42°, Pacific reference meridian −120°): the longitude correction is (−122.42 + 120) × 4 ≈ −10 minutes — when local clocks read 12:00, True Solar Time is about 11:50 (plus the day’s Equation of Time).

Related reading: Born Overseas: Finding Your Correct BaZi Hour, True Solar Time Explained.