ZoneMapzone World Clock

Hacker News

I built this because I kept needing to answer "when is 3pm EST for my teammate in Singapore" and none of the existing tools felt right for me - they're mostly lists. I wanted a map where time differences are spatially obvious. A few things that were technically interesting to build: The day/night terminator. It's not just a shaded half-sphere. I implemented a simplified USNO solar declination algorithm, computing the subsolar point for a given UTC timestamp, then tracing the great-circle terminator and sampling which side each pixel falls on. It renders pixel-by-pixel onto a Canvas overlay above the SVG map. During drag it bypasses React's render cycle entirely and draws directly on the canvas ref for zero-latency feedback. The map drag = time scrub. Dragging the map horizontally shifts time - one full map width equals 24 hours (1440 minutes). The math is straightforward (pixel delta → minute delta → new Date), but making it feel fluid required some care. City card updates use useDeferredValue so the main thread prioritizes the drag over re-rendering all the cards. URL state. The current city list, base city, and manual time are encoded in the URL and debounced at 500ms so you can share or bookmark a specific view. Restoring from URL has to deal with two city sources: ~306 hardcoded IANA cities and ~33k GeoNames cities that live in localStorage after a search. The GeoNames dataset was 33,334 cities after deduplication-by-timezone. I build a JSON file at deploy time rather than hitting the GeoNames API at runtime. Stack: React 18, TypeScript strict, Vite, Tailwind, Framer Motion, D3-geo Mercator, date-fns-tz, Hono for the city search API. MIT licensed. Source: https://github.com/zzjoey/ZoneMap Live: https://zonemap.live Known rough edges: mobile layout is functional but cramped, and the terminator calculation skips atmospheric refraction so it's off by ~0.5° at the poles.

Visit product View on Hacker NewsFeb 25, 2026

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TrustMRRLess likely to generate early MRR · Missing: mobile apps, ios, personal

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Acquire.comPre-revenue stage for this audience · Missing: arr, mrr, revenue

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BetaListMay not resonate with beta-testers · Missing: web3, chat, crypto

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