( Source of summary text, including Ringworld parameters) Ringworld has a habitable flat inner surface equivalent in area to approximately three million Earth-sized planets. It rotates, providing an artificial gravity equivalent to 99.2% of Earth's gravity by way of centrifugal force. The 'Ringworld' is an artificial ring about one million miles wide and approximately the diameter of Earth's orbit (which makes it about 600 million miles in circumference), encircling a Sol-type star. This document assumes the reader is familiar with the Ringworld, a megastructure located outside of Known Space but in brief: DISTRIBUTION IS PROHIBITED AND PUNISHABLE BY LAW. NOTE: THIS DOCUMENT IS CONFIDENTIAL, AND THE PROPERTY OF THE UNITED NATIONS AMALGAMATED REGIONAL MILITIA. The format of this answer is currently under discussion in meta.

I've done my best to keep the 'facts' correct and sourced from the Ringworld novels, but this 'document' is my own invention. Note: This answer is written in the form of a fictional, in-universe briefing document.

Or they could have given the Ringwall a distinctive, irregular, zigzag rim, like mountain peaks, so that one could do basic navigation by measuring the angles to distinctive Ringwall peaks (as is done in coastal navigation) this would only work near the Ringwall though not a chance of seeing it through 100'000 km of atmosphere.

The Engineers might have thought about embedding radio-emitting marker beacons into scrith in a regularly spaced, tight network, each one emitting its position, every 1000km or so.

I suppose one could use extremely exact inertial navigation (but won't the integrator be mightily confused by being on a rapidly rotating ring?).Firstly, there is no practical way to navigate by the stars (or is there?).So how would one determine one's position on the ring? I thought about the following: Of course, there are some distinctive places one can easily identify, like Mons Olympus on the Map of Mars, but these are far and few between. Meeting places are hard to find ('We will meet exactly 1650'000 km spinward and 244'000 km to port, next to a small forest'). It recently occurred to me that trips on the Ringworld have a problem: The Ringworld is so vast that finding out where one exactly is at any moment is fraught with difficulties. A long,long time ago I read Larry Niven's 'Ringworld' and 'The Ringworld Engineers'.

Larry niven ring world