Many states run a free or cheap RTNReal-time network. A group of base stations spread across an area that work together to send RTK corrections.More. RTN means real-time network: a group of Base stationA GNSS receiver sitting still on a known spot. It figures out how wrong the satellite signals are right now and shares that as corrections.More spread across the state that all send CorrectionsLive info from a base station about how far off the satellite signals are, so your rover can cancel out the error.More. The state's transportation department (DOTDepartment of Transportation. The state agency that runs many of the free state RTK networks.More) usually runs it. Private and nationwide companies fill the gaps or add extras.
| What to compare | Free state network | Paid private or nationwide |
|---|---|---|
| Cost | Free or a small fee. You usually still have to sign up. | A monthly or yearly subscription |
| Datum | Usually NAD 83(2011)The official US datum for horizontal position right now. Most state networks give coordinates in it.More, tied to the official national system | It varies. Some use ITRFInternational Terrestrial Reference Frame. A worldwide datum. In the US it's about a meter different from NAD 83.More, so check. |
| Coverage | Inside that state, plus a little past the edges | Many states or the whole country |
| Help when it breaks | Best effort | Usually a support line and an uptime promise |
| How close the stations are | Varies a lot by state | Varies. Dense in some areas. |
Work in more than one state? One multi-state subscription can be easier than keeping several state accounts. Every state page lists every option side by side. Start at the state map, see prices on the compare page, or let the Which service fits me picker rank them.