The Imperial Palace loop, measured for runners

Runners in central Tokyo count laps of the moat road. The lap is the unit, and the convention that matters most on it is a direction, not a corner. Everyone goes counterclockwise, and the curated route data stores the other one.

What the loop measures

5.07 km, closed on itself, paved, four turns.

That is what the curated route data stores for the Imperial Palace loop, and it is close to the figure the ward's own tourism body publishes. The Chiyoda City Tourism Association writes that one lap around the palace is roughly 5 kilometers, checked 2 August 2026.

Two of those fields do more work than the distance. The route is stored as a closed loop, so the start and the finish are the same point and you can begin anywhere on it. The surface value is paved for the whole line, which is as much as the data says about the ground: routes are recorded as either paved or mixed, and nothing finer. The estimated time is derived from the shape and stored beside it, not a time anyone ran.

Four corners across five kilometres

That is very little instruction for the distance.

A bend becomes a turn only when the direction of travel changes by at least 55 degrees measured 35 m before and after it, and the same 55 degrees must still hold when the angle is re-measured over a wider 56 m window. Anything shallower never enters the count. The number is a property of how corners are counted, and not a verdict on the road.

Turns that survive that test are sorted into six kinds. 55 to 75 degrees is bear left or bear right, 75 to 160 degrees is turn left or turn right, and above 160 degrees is a U-turn. There is no seventh category, so every corner on the loop resolves to one of those phrases.

Two things fall out of that list. The corners are bunched into the middle of the lap: 0.68 km from the first to the second, 0.88 km on to the third and 1.52 km on to the fourth, which leaves a gap of almost 2 km from the fourth corner round to the first, and nothing is spoken about a corner until 120 m before it. Those offsets are measured from the point where the stored line begins, which is not a start line on the ground, so what carries over to a lap you join somewhere else is the spacing. The offsets do not. The other thing is that the classification sits close to its own boundaries here: the stored bearings put the second corner at 55 degrees of change, just inside the bear right band, and the third at 76 degrees, just past the point where bear right becomes turn right.

Count the corners before you count the kilometres. A park circuit stitched together from footpaths collects instructions, and a single continuous perimeter road does not, whatever their lengths are. If you want a route that leaves you alone while you run it, the turn column is the one to read. The trade is the whole subject of city routes and turn cues.

Which way round, and why it matters to your app

Counterclockwise.

The Chiyoda City Tourism Association states it plainly, that everyone is running counterclockwise, and publishes it beside the rest of the etiquette for the course. That etiquette covers pedestrians and the no running areas at the main sightseeing spots, which it notes tend to be very crowded. Checked 2 August 2026.

Runflake's curated version of the loop stores one direction of travel, and it is the other one. All four of its stored corners are right turns, and a closed line whose every corner turns right is a line that closes clockwise.

So the curated route runs clockwise around the moat, and a lap run the way the etiquette describes is a lap run against the stored direction.

Which direction is stored matters because of what the app does with it, not because of the corners themselves. Turn instructions are computed for the stored direction, and on the ground they arrive in a fixed sequence.

1. On screen from 400 mThe next turn appears on the screen earlier than the voice says anything, on the reasoning that a screen you choose to look at cannot interrupt you.
2. Spoken at 120 mEach turn is announced at most twice. The first call comes at the route's pre-announce distance, which is 120 m on every curated route and is clamped to a range of 40 m to 300 m.
3. Repeated at 25 mThe second call comes 25 m before the corner, and it is skipped when the first call was already closer than 50 m, so you are not told the same thing twice inside a few strides.

Spoken distances are rounded down before they are read out: to the nearest 50 m in metric, or the nearest 10 m below 100 m, and to the nearest 50 ft in imperial. So you hear a round number and never an oddity like In 117 meters. Direction is settled before any of this begins: at the start of a course run no turn is announced until the app has seen 60 m of forward progress, and until then the screen says: Working out which way you are running.

Running it in reverse, and what stops

Turn cues stop.

Run a curated course backwards in Runflake and the cues switch off entirely, with the reason on screen: You are running this course in reverse, so turn cues are off. They are not mirrored, because a bear right and a U-turn do not become correct instructions by being flipped, and a wrong instruction at a junction is worse than silence.

The rest of the run carries on.

• Recording continues.
• The distance announcement still fires on every completed kilometre, and splits are muted only while you are off the route, not when you run it the other way. The map keeps drawing the course line and not your own trace while you are following a course, so the route is still there to follow by eye.
• Completion is the thing that stops. The course will not be marked as completed, and completion needs at least nine tenths of the route covered, measured as the union of the stretches you actually passed, the finish reached within 50 m, no mock location flag on the run, and fewer than half the samples judged to be running backwards.

On this loop that is not hypothetical. The stored direction is clockwise and the etiquette is counterclockwise, so a runner doing the conventional lap as a course run is the reverse case, and the four corner calls do not come. The recording is not affected, and on a single closed loop with no junctions to miss there is little for those calls to do anyway. Know that before you spend a lap waiting for a voice the screen has already told you is off.

Where to start if you arrive by train

Anywhere on it.

A closed loop has no official start line. That is the practical advantage of this route over a point to point: you join wherever you reach street level, and that point becomes both your start and your finish.

What your choice does change is where your split calls land. In metric the distance announcement fires on every completed kilometre, and the kilometre is a fixed 1,000 m constant rather than a setting you can move. On a 5.07 km lap the markers therefore sit wherever you began, each further lap pushes them about 70 m further round, and after three laps the last kilometre call lands about 210 m before your line. Two runners who joined the loop at different points hear their third kilometre nowhere near each other, and neither of them is wrong.

• Pick a fixed object at the point you join, a gate, a bridge or a signboard, and start there every time. A repeatable line is worth more than a convenient one, and the first kilometre off it should be a running kilometre.
• So walk the last stretch to that line.
• Run the convention, not your preference. Counterclockwise, watching for pedestrians, and off the pace entirely at the crowded sightseeing points.

Where the route data comes from

OpenStreetMap, under the Open Database License.

The shapes are credited to OpenStreetMap contributors, and the project's own copyright page states the condition in one line, that you are free to copy, distribute, transmit and adapt the data as long as you credit OpenStreetMap and its contributors. Checked 2 August 2026.

Corners are not part of that download. Turn instructions are computed from each route's own shape by Runflake's own turn detector before the route is published, and none of them is written by hand or taken from a navigation provider. That is why the count for a route is a measurement of its geometry and not an editorial judgement, and why a route can legitimately come out at zero.

A route with no turns is treated as a fact rather than a failure. In that case the app says: This course has no turn guidance. Follow the route on the map. It keeps that separate from the case where the guidance failed to load, which reads: Turn guidance could not be loaded for this course, so this run has no turn cues. The difference matters when you are standing at a junction deciding whether to trust the silence.

Using it as a repeatable session

Treat the lap as the unit and the arithmetic does the planning for you. One lap is 5.07 km, two laps 10.14 km, three laps 15.21 km, and because the surface and the corners repeat exactly, lap two is comparable to lap one in a way that two different five kilometre routes never are. The loop is the control, so the only variable left is you.

• Steady single lap: one lap at a pace you could hold for two. The value is the reference time, not the effort.
• Progressive double: second lap faster.
• Corner surges: the gaps between corners are 0.68 km, 0.88 km and 1.52 km, with almost 2 km from the last one back to the first. Lift the pace out of each corner and settle back before the next.
• Time trial: one lap flat out, always from the same fixed line, run at the same time of day so the crowding is comparable.

One practical warning about listening to splits on a loop. Your kilometre calls and your laps will never line up, because 5.07 does not divide into whole kilometres, and after three laps the drift is a little over 200 m. If you are pacing off the voice, pace off the split it reads out and not off the landmark you happen to be passing when you hear it. What running apps say out loud covers what those announcements contain and in what order.