HistoryLayer is a map you can read without an account. An account exists so that what you keep can follow you between devices, and it stores what that needs.
This page describes what is collected as things stand. It is a description rather than a set of promises: if what is collected changes, this page changes with it, and the date at the foot says when it was last true.
If you never sign in
The map, the events and the people are public files and public read-only endpoints. Reading them involves no account, and the site stores nothing against you beyond the request log described below.
Some things are kept in your own browser and are not sent to the server:
-
How you like to read — which categories are switched on, how much
border detail, light or dark, whether the people layer is showing,
how wide the side panel is. These are
localStorageentries such ashistoryMapFiltersandappearance.choice. -
A picture on its way to the atlas, while it is on its way. An editor
adding one writes it to an
IndexedDBstore in this browser first, so the panel can draw it without waiting, and it is removed from there once the upload has landed. The picture itself is uploaded and becomes part of the record, visible to every reader — see below.
Clearing your browser's site data for this domain removes all of it.
If you have an account
| What is stored | Why |
|---|---|
| Your email address | It is how you sign in, and how an account is told apart from another. |
| A hash of your password, if you set one | Hashed with scrypt and a per-account salt. The password itself is never written down, and cannot be recovered from what is — not by us either. |
| A display name, if you give one | So the account is called something other than an email address. |
| Sessions | A random token in a cookie your browser holds and this site's JavaScript cannot read. It expires after 30 days, and signing out deletes it on the server rather than only in your browser. |
| Pictures you upload, if you are an editor | A picture put on a record is stored on the server and served to every reader, because that is what putting it on a record means. It is filed under a hash of its own contents, so the same file uploaded twice is stored once, and the account that uploaded it is recorded alongside it. Only editors and admins can do this; signed in as anyone else, the control is not offered. |
| What you have saved | The events and people you starred, with the title and year they had. |
| Your notes | Yours: they are shown back to you and are not part of the map anybody else reads. |
| Corrections you propose | These are not private: a correction that is accepted changes what everybody sees, and the record of who proposed it is part of how that is answerable. |
| The time you last signed in | To find abandoned accounts and unused sessions. |
Signing in with Google
If you use the Google button, Google tells this site three things: a stable identifier for your Google account, your email address, and whether Google has verified that address. Your name comes with it if your Google profile has one. Nothing else is requested — not your contacts, not your calendar, not your files — and the permission screen Google shows you will say so.
That identifier is stored so the same Google account signs you back into the same HistoryLayer account. If the address is one Google has verified and an account here already uses it, the two are joined, so you do not end up with two accounts and half your saves in each. If Google says the address is not verified, they are deliberately not joined, because otherwise registering somebody else's address somewhere would be a way into their account.
Signing in with Google does not give this site access to anything in your Google account, and it does not let Google see what you do here.
How many people visit
We do look at how busy the site is. That number comes from the request log that Vercel, which serves the site, keeps for every site it hosts — the same log any web server writes. Each line records the ordinary things a server sees: an IP address, which page was asked for, the browser's user agent, roughly where in the world the request came from, and how long it took to answer.
What is taken from it is how many visits there were. The logs themselves are Vercel's, kept and discarded on their schedule rather than ours.
Three measurements run in your browser
Alongside that log, two scripts count page views from your side of the connection. Both are cookieless: neither stores anything in your browser, and neither can recognise you on another site.
The third is different, and it is the one worth reading about. PostHog records a short list of things done with the map — a year settled on, a region selected, a record opened by name, the detailed map chosen, a search and the words it was made with — so that it is possible to tell which of the fifty-four maps people actually read, which records are worth writing more of, and which parts of this go unused. Unlike the two counters, it does keep a random id in your browser, which is how a second visit is recognised as a second visit rather than a new one. That id says nothing about who you are and is not joined to an account.
What it deliberately does not do is worth saying as plainly. It does not record your screen: session replay is switched off in the code rather than left to a setting. It does not capture clicks by itself — the handful of events below are written out by hand, and nothing reads the text of the page to label them. It builds no profile for a reader, only for signed-in editors, and this site never tells it who they are. It is off entirely if your browser sends Do Not Track or Global Privacy Control, and it is loaded only after the map has finished drawing.
| What | Where it comes from | What it sends |
|---|---|---|
| Vercel Web Analytics | A tag on the map page. It is fetched from this domain rather than from Vercel, and it is not on this page, the licence page or the guide — none of the three carries any measurement. | The page viewed, where you arrived from, your country, and the broad type of browser, operating system and device. |
| PostHog (US) | A module in this site's own code, sent from this domain and loaded only once the map has been drawn. Not on this page, the licence page or the guide. The only script those three carry is the one that reads your light-or-dark choice out of this browser so the page matches the map; it sends nothing anywhere. | The page viewed and left, and a named event for each of: a year settled on for a second or more, with its era, and the year you asked for when this atlas had no map of it; a region selected, by name; a record opened, by name, with its year, category, whether the account was written for this project, and whether you opened it in the sidebar or read it in full; a record saved; the categories left switched on; the map type chosen; and a search being opened, with what was searched for and whether it found anything. So this one does record which events, people, wars and places you opened, and what you typed into the search box. Searches are kept because what people look for and do not find is the clearest signal of what this atlas is still missing. Nothing else you type is sent — not a note, not anything in the editing tools — and it does not record your screen. It keeps a random id in your browser so a return visit is recognised as one. Held in the United States. |
| Cloudflare Web Analytics | Added by Cloudflare as the page passes through it. It is not part of this site's code and does not appear in its source; Cloudflare inserts it in transit because the setting is switched on there. | The page viewed, where you arrived from, your country, the broad browser and device, and how quickly the page loaded and became usable. |
None of the three is joined to your account, and nothing on this site sends any of them your email address, what you have saved, or what you have written. The first two are aggregate counters and cannot tell one reader from another at all; the third can tell a returning browser from a new one, and that is the whole of what it knows about you.
Who else is involved
Running the site means other companies handle the traffic, and they can see the ordinary things any web server sees — your IP address, the page you asked for, and your browser's user agent — in their own logs.
| Who | What for |
|---|---|
| Vercel | Serves the site and runs the API, keeps the request log, and runs the other page-view counter. |
| PostHog | Receives the map events described above, in the United States. |
| Neon | Hosts the database, in the United States (us-east-1). |
| Cloudflare | DNS, sits in front as a cache, and runs one of the two page-view counters described above. |
| Only if you choose the Google sign-in button. |
Your browser also fetches things directly from servers that are not ours, which means those servers see your IP address in the same ordinary way. They are told nothing about your account:
- Wikimedia Commons and Wikipedia — the pictures and the written descriptions on records.
- GitHub Pages — the historical border geometry, which is served from its own repository for licensing reasons.
- Esri / ArcGIS — the base map behind the location picker, and only if you use the editing tools.
How long things are kept
- Sessions expire 30 days after they are created, and signing out ends one immediately.
- Saves and notes are kept until you remove them or the account goes.
- Deleting an account removes its sessions, saves, notes and provider identities with it.
- Corrections that were accepted stay, because they are part of the map's history rather than part of your account. They can be detached from your account on request.
Getting a copy, or getting rid of it
Ask, and you can have a copy of everything stored against your account, or have the account deleted. There is no self-service button for either yet; both are done by hand, which is honest about the size of this project rather than an obstacle. Write to [email protected].
Depending on where you live you may also have the right to correct what is stored, to object to it, or to complain to a data protection authority. Nothing above is meant to narrow that.
Children
The map is for everybody. Accounts are not intended for children under 13, and none of the site's content requires one.
If this changes
Any change to what is collected will be described here, with the date below updated. If a change is significant — a new third party, a new category of data — it will be said plainly on the site and not only on this page.
Last updated 19 August 2026. HistoryLayer is run by Novark Works. Questions: [email protected]. See also sources and licences.