How the map works

On a first visit the map asks your browser where you are and opens there. How far it zooms in depends on how sure the answer is: a phone outdoors gets a close view, while a browser guessing from your internet connection gets a wider one rather than a street corner that may be nowhere near you.

Say no and the map simply opens where it was going to anyway. Nothing else changes, and the locate button in the corner of the map still works if you change your mind.

It only does this when nothing else in the link says where to look. A shared view, a shared pin, or a reload of a map you had already moved all open where they point.

The search box above the map takes a place name and finds towns, campgrounds, trailheads and the like, preferring places near the view you are looking at, because half the creeks in the country share a name.

It searches your own saved work first and shows it at the top, marked as yours: waypoints, tracks and whole folders, by name and by note. That part needs no signal, so it still answers with the phone in aeroplane mode.

On a free account, place search and the nearest town shown for a pin come from OpenStreetMap, through Photon, a free service run by komoot. It finds towns, peaks, lakes, parks, campgrounds, trailheads and roads well. Businesses and street addresses it finds less reliably, because OpenStreetMap is mapped by volunteers and many shops and house numbers are not in it yet.

Premium search asks Mapbox and OpenStreetMap together. Mapbox knows far more businesses and street addresses, so its results come first and appear straight away; OpenStreetMap often knows the ground a photographer goes to that Mapbox does not, such as a named arch, a spring or a trailhead, so the places only it has are added underneath a moment later. A place both know is listed once. Mapbox charges for every search, which is why it is part of Premium rather than free.

The search box also takes a coordinate, in any of the three forms the details panel prints, so anything you read off this app can be pasted straight back into it:

• 35.960000, -84.280000 — decimal degrees
• 35°57.600'N 84°16.800'W — degrees and decimal minutes, what most handheld GPS units show
• 35°57'36.0"N 84°16'48.0"W — degrees, minutes and seconds, as printed on paper maps

The punctuation is taken loosely. Degree signs are optional, a comma and a space work the same, and N, S, E and W can sit on either side of their number or be left out in favour of a minus sign.

Latitude comes first unless the first number is too large to be one, in which case it is read as a longitude and the result says so. The result always shows the coordinate written back out in full, so you can see what it read before you go there.

This is arithmetic, not a lookup, so it works with no signal.

Select a pin, or press anywhere on the map, and choose Details. The Photography section lists sunrise and sunset times with their angles, plus golden hour and blue hour times and durations.

Buttons there open light phases, the moon, the Milky Way — where the night is scored out of moonlight and cloud cover — the aurora, eclipse timing, and fog likelihood and type. A last button, Draw, puts the night on the map itself: the bearings where the sun and moon rise and set, where each of them is at this moment, and the Milky Way band and its core.

All of it is worked out for the coordinates of that pin rather than the nearest city, and it is arithmetic rather than a lookup. There is no request behind it, so it answers the same on a ridge with no bars as it does at the kitchen table.

Moon. Rise and set, the phase, and the percentage lit. The phase is named the way an almanac names it — new, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, last quarter, waning crescent — and the percentage is how much of the disc is lit, which is a different number from where the moon is in its cycle. Waxing or waning is the useful half of it: it tells you whether tomorrow night will be brighter than tonight or darker, which is what decides whether to go now or wait a week.

Milky Way. Whether the galactic core is up tonight, how high it climbs, the window while the sky is properly dark, and the best nights over the coming weeks. The night is also scored out of two things that can ruin it — how much moon is up during that window, and the cloud cover forecast across it.

Aurora. The chance at your latitude, sourced from NOAA, along with the Kp index. Both feeds come from NOAA’s Space Weather Prediction Center: the chance is read out of the OVATION model, which publishes a whole-globe grid of aurora probability, and the Kp index comes from the planetary K-index feed beside it. Kp is a 0–9 scale of how disturbed the Earth’s magnetic field is, and it matters because it decides how far south the aurora reaches: 4 is unsettled and worth a look north from the northern states, 5 is the storm line, and 7 and above is the rare kind that is visible well south of it. Worth knowing what the model is answering: OVATION says where the aurora is, not whether you will see it. Cloud, the moon and whatever is standing on your northern horizon all still apply.

Eclipse. The next lunar eclipse, its contact times, and whether the moon clears your horizon for them. A lunar eclipse is one event the entire night side of the planet sees at the same moment, so it resolves to arithmetic. Where a solar eclipse falls is a fussier calculation, and Halfstop does not attempt it.

Fog. An hour-by-hour likelihood, with the kind named beside it. Ground fog forms in place: the ground radiates its heat away under a clear sky, cools the air touching it past its dewpoint, and a light stir spreads that cooling up through a layer deep enough to see. It needs night, a clear sky, and wind that is light but not absent — dead calm makes dew instead — and it is what fills a hollow or a river bottom by dawn and burns off an hour or two after the sun reaches it. Drifting fog is carried in: moist air moving over colder ground, cooling from below as it travels. It needs more wind than ground fog tolerates, ignores the sky and the hour, comes off water and off spring snowpack, and leaves when the wind changes rather than on any schedule. Either can be freezing fog when it happens at or below freezing, which is called out separately because it says nothing about how the fog formed and everything about what it will do to a road and a tripod.

Two kinds are missing on purpose. Upslope fog turns on the wind’s direction against the shape of the ground, and steam fog turns on the temperature of the water it comes off; neither of those is in the forecast feed, and guessing at them would be inventing a forecast rather than reading one. A lake shore or a steep hollow will fog when this says it will not.

The last tab draws the plan on the ground: bearings from the pin to the sun, to the moon and to the galactic core, with the Milky Way band itself as the wide curve. The slider moves time, and the lines swing with it.

That is the point of drawing them. A table can tell you the sun comes up on a bearing of 71°; only the map tells you the ridge is in the way.

Select a saved waypoint, choose Details, and the Photos section has Add photos and Take one. On a phone, Take one opens the camera.

Pictures are resized on the way in: 1024 pixels on the long edge, under 100 KB each. That is full width on a phone screen, and small enough that a folder with a hundred of them still opens quickly. A photograph already smaller than that is kept exactly as it arrived.

JPEG, PNG, WebP, GIF and AVIF always work, and any other picture your browser can open - BMP or TIFF, say - is converted on the way in. iPhone photos (HEIC) work from an iPhone, which converts them to JPEG as you add them, and in Safari on a Mac. Chrome and Firefox cannot open HEIC; there, save the photo as a JPEG first. RAW files (DNG, NEF, CR3 and the like) need exporting as JPEG before they can be added.

They stay on the device they were added to. Nothing is uploaded, which is also why they do not appear on your other devices.

Light pollution and sky brightness are both selectable as a layer under the Conditions group. They are not the same measurement: light pollution is what the satellite sees looking down, which is a good proxy for what to point a camera away from, while sky brightness is modeled looking up and is given as a Bortle class. Turn them on to pick the ground before you plan the night, then fade them back so you can see the roads under them.

Saves the area you are looking at as a named region, recording the bounding box, a zoom range and the basemap that was showing.

Three other ways to mark the ground: Draw a region to drag a rectangle across the map, or Set by hand for a region round the middle of the map, round a coordinate you type, or round every place in a folder, reaching as far as you choose. The folder one is the one a trip wants: all its pins and the roads between them, without a box that misses the one at the edge. The region is outlined on the map before you save it.

The regions you have marked. Each one shows the ground it covers, the tile count at your chosen zoom range, and roughly how much space it will take.

Open Adjust the edges on a region to type over its north, south, east or west edge in degrees, or to move all four to the edges of the map as it is now. Download it again afterwards to fetch the new ground; what was already stored is kept.

Fetches the tiles and keeps them on the device. It stores the selected basemap plus any layers switched on over it, and the panel names everything it is about to store before you press it.

Afterwards each region says when it was downloaded and how many tiles it holds, in the download menu and under Saved for offline in Folders. Each time you look, it checks the tiles are still on this device. If the browser has cleared them, the region says so in red, and Download again fetches them back.

Byways Topo, USGS Topo and Imagery, the state aerial and lidar layers, BLM, and the FAA ceilings.

A browser treats what a website stores as something it may clear when the device runs short of space. So the first time you download a region, Halfstop asks the browser to keep its storage until you delete it, and the storage line under your regions says whether it agreed. Firefox asks you; Chrome, Brave and Edge decide for themselves.

The surest way to keep them is to install Halfstop: in Chrome or Brave on Android, the menu then Add to Home screen or Install app; on an iPhone, Share then Add to Home Screen. An installed site is far less likely to be cleared, and on an iPhone it is exempt from Safari clearing a site's storage after seven days without a visit.

A browser set to clear site data when it closes clears downloads with it. In Brave, keep app.halfstop.app out of Forget me when I close this site and any clear-on-exit setting.

Before a trip, open the map once on good Wi-Fi, download your regions, then switch to airplane mode and check the map still draws there.

Downloads stay where you made them. On an iPhone, Safari and Halfstop on the Home Screen each keep their own storage, so a region downloaded in one is not in the other, and removing Halfstop from the Home Screen removes what it downloaded. The same goes for the Android app and a browser on the same phone.

In the Android app none of this applies: downloads stay until you delete them or uninstall the app.

A photograph of the map as it looks right now, saved to your device. It is not the same as a downloaded region: a picture cannot be panned or zoomed, but it needs no account, no network and almost no space.

The share button in the top menu bar copies a link to exactly what you are looking at: the maps you have open, the basemap under them, and the view itself.

A saved waypoint or a dropped pin has its own Share. The link opens the map over that coordinate with the name on screen.

Open the folder's menu (the pencil beside it) and press Share. Three ways to send a copy:

• Send a link - the easiest. It opens the places on a map in any browser, on any phone or computer, with nothing to install, and offers to save them to their own folders. It works for thirty days, and shows the folder as it was when you sent it. You need to be signed in to send one; the person opening it does not.
• GPX file - for Gaia GPS, Garmin, OsmAnd and almost every other map app.
• GeoJSON file - every property on every pin, for another map or a script.

A phone does not open a file by itself; it needs an app that reads one. With the Android app installed, tapping a GPX or GeoJSON in Gmail, Messages or Files offers Open with Halfstop. Anywhere else, save the file, then open it in Halfstop as any other file.

Sending a copy is not sharing the folder itself. To have somebody see your changes as you make them, or work on it with you, invite them instead - that is part of Premium, the folder has to be synced to your account, and the person you invite only needs a free account. See working on a folder together.

Invite someone to a folder as a viewer or an editor. An editor can add, change and remove waypoints, and both of you keep your work. Waypoints merge one at a time rather than the newer save taking the whole folder, so your new pin survives while they rename a different one. If you both change the same waypoint, the later change stands.

The folder stays yours. An invitee cannot delete it, refile it into their own folders, or pass it on to anyone else. Withdraw the invitation at any time and it leaves their device on their next sync.

It changes on your plan. If your Premium ends, the people you invited can still see the folder as it was, and nobody can change it until you subscribe again.

A trip is a folder with dates on it, so all of this applies to trips as well, and the dates travel between your own devices along with everything else.

Drop the file onto the map, or open Files on the map in the side panel and click to choose one. GPX, KML, KMZ and GeoJSON all work, from Gaia GPS, CalTopo, Google My Maps, a GPS unit or anywhere else that exports them, and so do the CSV lists Google Takeout exports (see Google Maps places). The file is read on your device and is not uploaded; file its waypoints into a folder to keep them.

In the Android app you can also start from the file: tap a GPX, KML, KMZ or GeoJSON in Gmail, Messages or Files and choose Halfstop under Open with. It opens on the map the same way.

Google Maps has no export button, but Google Takeout exports your places. Go to takeout.google.com, choose Deselect all, tick Maps (your places) and Saved, and create the export. Google emails you a link to a zip file.

Starred places are in Saved Places.json. Open that file the same way and they arrive with their names, your notes, their addresses and a link back to Google Maps. Google exports a few places with no location at all; Halfstop names those rather than putting them in the sea, and you can add them by hand.

Lists such as Want to go, Favorites or your own are in the Saved folder, one CSV file per list. Open the CSV the same way. Google leaves the locations out of those files, so Halfstop places each one from its Google link where the link carries a position, and otherwise looks it up by name: in OpenStreetMap on a free account, and in Mapbox on Premium. Before anything is saved you see every place with what it matched, can pick a different match or untick one, and anything not found is named. A name can match somewhere else, so check chains and common names before you rely on them.

If you would rather Google did the matching, open Google My Maps, create a map, choose Import, pick the list's CSV and choose Title as the column that says where each place is. Then ⋮ → Export to KML/KMZ gives you a file Halfstop opens.

Maps you made in Google My Maps export the same way, straight to KML or KMZ.

One basemap at a time — it is the ground everything else is drawn on. Overlays stack over it in any number, each with its own switch and its own opacity, so public land, forest roads, weather and airspace can be turned up or faded back without disturbing the map underneath.

A red badge means that layer’s service is not answering. Some are known to be intermittent.

Nothing here is a flight authorization. It is the FAA’s own data drawn on a different map, and it can be out of date.

The UAS Facility Map: the grid LAANC reads when it approves a flight. The number is how high LAANC will grant that authorization instantly — not a speed limit for the sky. Every cell on the grid is inside controlled airspace, and a Part 107 flight there needs authorization whatever the cell says. A ceiling of 0 does not mean the airspace is closed; it means nothing is pre-approved and the request goes to further coordination or FAA DroneZone instead.

Outside controlled airspace there is no grid at all. That is Class G, where no authorization is needed — an absent cell is an answer, not a gap.

Red is do-not-fly: airspace where flight is prohibited or restricted.

Amber asks for care rather than permission, and it covers two different things. Over wilderness and Park Service land, flying across is not itself prohibited — taking off, landing and operating from the ground are. It means find somewhere else to stand, not somewhere else to fly. Alert and warning areas restrict nothing at all; they mark where other aircraft are doing something unusual.

Same-day temporary flight restrictions, such as wildfires and VIP movements, are NOTAMs and are not carried here. Check the FAA’s current advisory list before you fly — the card links to it.

Military operating areas are left out on purpose. They do not restrict civilian flight, and their floors generally sit well above where a drone flies.

Give it your stops and it works out the distances between them, how many days that adds up to, and where each day breaks. It also draws the actual road route.

Not today. Halfstop is built for planning and photography rather than navigation, and turn-by-turn would mean metered routing services that push the subscription price up.

Not for browsing, planning or drawing on the map, or for saving folders on this device. An account is needed to sync them between devices, and to open a folder somebody shares with you. Both work on a free account.

Signed in, your folders follow you. Sign out and they are cleared from that device, because they live on your account and come back the moment you sign in again. If the last sync did not go through, or a free account holds more than it syncs, they stay put instead, and the panel says so.

Folders and the pins inside them.

A free account syncs up to 100 folders and 100 waypoints. A track counts as one waypoint however long it is, and a folder somebody shared with you does not count at all. Past that, your folders stay on the device you made them on, the panel says so, and nothing is deleted. Removing some brings you back under, and Premium syncs any number.

Why a limit: every folder on the server is storage and every sync is bandwidth, which cost money each time. A hundred waypoints costs next to nothing to carry, and is enough to see whether syncing is worth paying for.

Photographs stay on the device they were added to — only the reference travels, so a picture taken on your phone will not appear on your laptop.

You stay signed in. Your sign-in is kept on this device, so losing signal does not sign you out, and nor does closing the page. The account panel says you are offline, your folders are all still there, and Premium works as it did the last time Halfstop could check, until the end date of your plan.

Changes you make while offline are kept on this device and sync on their own once there is a signal again. Nothing about your sign-in runs out while you are away; it is renewed the next time Halfstop can reach the server.

You are signed out when you sign out, and signing out with no signal still signs you out of this device straight away.

GPX by default, which is what Garmin, Gaia, AllTrails and every handheld will import. GeoJSON is offered alongside it for anything that wants the full properties.

Whenever you like, without asking anybody.

If you subscribed here, open Manage subscription on your account page. It is also under Plan in the settings menu, the gear at the top of any page including this one. Either one opens the payment provider’s own pages, where you can also switch between monthly and yearly or change the card.

If you subscribed through the App Store, Apple handles it instead: Settings, your name, Subscriptions. Only Apple can end an App Store subscription.

If you subscribed in the Android app, Google Play handles it: the Manage subscription button opens it, or in the Play Store, your profile picture, Payments and subscriptions. Only Google can end a Google Play subscription.

Canceling stops the next payment rather than cutting you off. Premium runs to the end of the period you have already paid for, then the account goes back to being a free one.

Nothing of yours is deleted. Folders, waypoints and notes all stay, and export keeps working, because getting your own data out is free and always will be. What stops is the metered part: folders past the free allowance of 100 folders and 100 waypoints stop travelling between devices, search goes back to OpenStreetMap, and the layers and downloads that cost money each time become unavailable again. Subscribe again and it all resumes.

Closing the account is a different thing and does delete everything. Cancel the subscription first, or you will carry on paying for an account that is not there.

This closes the account and removes your folders and pins from the server. Signing in again will not bring any of it back. What is saved on this device is left alone, and export works right up until you press it, so take a GPX first if you want one.

If you pay for Premium, cancel the subscription before closing the account. Closing it does not stop a subscription bought through the App Store or Google Play. Only Apple or Google can do that.

It is here rather than on the account page on purpose. It is the one thing in this app that cannot be undone, and a button that ends an account does not belong next to the one that signs you out of it.

Halfstop for Android is open for testing. Install it from Google Play.

It is the same atlas as this site. Sign in with the same account and your folders come with it, and so does Premium, wherever you bought it. Premium can also be bought inside the app, through Google Play.

It is a test release, so expect the odd rough edge. If something breaks or reads wrong, write to support@halfstop.app with the phone you are using and what happened. That is what the test is for.

An iPhone app on the App Store is next. Until then, the site works in Safari, and Add to Home Screen gives it an icon of its own.

Write to support@halfstop.app. That is the whole process. There is no form to fill in and no account needed to send one — if the thing that is wrong is that you cannot sign in, you can still write.

What makes an answer quicker: which page or screen you were on, what you expected, and what happened instead. A screenshot usually says it faster than a paragraph. If it is something on the map, roughly where — a place name or a coordinate — and which layers were switched on, because a lot of what looks like a map problem is one layer not having data over that ground.

Mail lands in a queue that one person reads, so a reply is not instant. Everything sent to that address is read.

The same address handles the things the terms and the privacy notice point at it for: a copy of your data, a correction, or a deletion you would rather not do with the button above.