How to Draw Points, Lines & Polygons on a Map
What is Capto?
Capto is a free, browser-based tool to graphically create geospatial data, accessible from any desktop or mobile device. Its purpose is to make it easy to draw, describe, and export points, lines, and polygons without installing anything or creating an account.
Key features:
- Draw points, lines, and polygons: Pick a geometry type from the toolbar and draw directly on the map.
- Custom attributes: Attach any number of key/value properties to a feature, in addition to its name.
- Layer management: Organize features into named, color-coded layers. Toggle visibility, labels, color, or delete layers at any time.
- Data persistence: Features, layers, and per-layer label settings are saved in your browser's IndexedDB storage and restored automatically on your next visit.
- Export to GeoJSON or KML: Download your features, with their custom attributes, in the format that suits your workflow — GeoJSON for GIS tools, KML for Google Earth.
- Current location: Place a point at your GPS position with one tap.
- Address search: Look up a place by name and jump straight to it, or add a point there.
How to use the Map Tools?
On the right edge of the screen you'll find a vertical toolbar (left edge, if you switch sides — see below). Each button controls a specific action:
The coordinates readout is separate from the toolbar: it sits at the top center of the screen. At the bottom center you'll find three more buttons — About, Help, and Disclaimer — always available regardless of what else is open.
How to search for an address?
- Click the Search address button search in the toolbar to open the search panel.
- Type a place name or address and press Enter or click the search icon.
- Matching results appear in a list below the search box. Click a result's text to center and zoom the map there — a small round marker previews the location.
- Click the add button next to a result to add a permanent point there. A dialog opens pre-filled with the place name; confirm to save it.
- The round preview marker disappears once you add the permanent point, or when you close the search panel.
- If nothing matches, the panel shows "No results".
Address search uses the free Nominatim geocoding service from OpenStreetMap and requires an internet connection.
How to draw a point, line, or polygon?
- Click the Draw point , Draw line polyline, or Draw polygon hexagon button in the toolbar. It will turn blue to indicate it is active.
- For a point: click or tap once on the map to place it.
- For a line or polygon: click once per vertex, then double-click (or tap the last point again) to finish the shape.
- A dialog will appear. Enter a name, select which layer it should belong to (if you have more than one), and optionally add custom properties (see below).
- Click Add feature to confirm, or Cancel to discard.
- Clicking a different draw button while one is already active switches tools without leaving draw mode.
How to draw a hole in a polygon?
Cut an interior opening out of an existing polygon — a building with a central courtyard, a plaza with a pond — with the Draw hole tool content_cut. It doesn't create a new feature; it adds a hole to one that already exists.
- Click the Draw hole button content_cut in the toolbar.
- Click inside the polygon you want to cut a hole into, to place the hole's first vertex.
- Continue clicking to add more vertices, then double-click (or tap the last point again) to finish the hole's shape — same as drawing a regular polygon.
- The hole is added immediately; there's no naming dialog, since it belongs to the polygon you clicked inside, not a new feature.
If the first click isn't inside any polygon, Capto shows an alert and cancels that attempt — the tool stays active so you can just click inside a polygon and try again, no need to reselect it from the toolbar.
A hole's vertices can be dragged, added to, or removed afterward with the Move feature tool, exactly like any other vertex (see "How to move or reshape a feature?" above). There's currently no dedicated way to remove an entire hole at once — deleting its vertices one by one with Alt+click eventually collapses it. Capto doesn't check that the hole you draw stays fully inside the polygon's outer edge, so keep it comfortably within the boundary.
How to snap to existing features while drawing?
While drawing or reshaping any point, line, or polygon, the cursor automatically snaps to vertices and edges of every other feature on a visible layer — no separate tool needed. Get close enough to an existing vertex or edge (a small cursor change is your cue) and click: the new vertex lands exactly on that coordinate instead of a few pixels off. This works for any combination of geometries — two neighboring polygons that share a real, identical boundary instead of a hairline gap; a line that starts exactly where another line ends, so a route stays continuous instead of nearly-touching; a line that starts exactly on a polygon's edge; and so on.
- Snapping works for both drawing (Draw point/line/polygon) and reshaping (Move feature) — it considers any feature on any visible layer, including other layers, not just the one you're drawing into.
- Hide a layer (visibility_off in the Layers panel) to stop snapping to its features without deleting them.
- Snapping targets both vertices and the edges between them, so you can also start a new shape exactly on the midpoint of an existing line or polygon side, not only at its corners.
How to add custom properties to a feature?
Any feature — point, line, or polygon — can carry custom key/value attributes in addition to its name, useful for anything a plain name can't capture (elevation, status, a survey date, a note).
- In the Add feature or Edit feature dialog, click + Add property below the Layer selector.
- A row with a Key field and a Value field appears. Fill in both — rows with an empty key are ignored.
- Click + Add property again for as many attributes as you need, or click the close next to a row to remove it.
- Properties are saved with the feature and included in both GeoJSON and KML exports.
If the feature's layer has a property schema defined (see "How to use layers?" below), its fields appear pre-filled automatically — you can still edit, remove, or add more beyond those.
Don't create a property called "name": every feature already has a built-in Name field (the one at the top of the dialog) — it doesn't need to be repeated as a custom property. A property literally named name would just duplicate it.
How to read coordinates on the map?
Click or tap anywhere on the map and its coordinates (latitude, longitude) appear in the readout at the top of the screen, with up to 7 decimal places — no feature needs to be selected.
- Click empty water, land, or any spot on the map to read that location's coordinates.
- Click a point to select it (it turns orange) and read its own exact coordinates.
- Click a line or polygon to select it — the readout shows "Multi-vertex feature selected" instead of a coordinate, since these geometries don't have a single coordinate of their own.
- Click the content_copy icon next to the coordinates to copy them to your clipboard.
How to move or reshape a feature?
The same Move feature tool handles repositioning a point and reshaping a line or polygon — there's no separate vertex-editing button.
- Click the Move feature button open_with in the toolbar. It turns blue when active.
- For a point: click and drag it to a new position.
- For a line or polygon: drag any existing vertex to move it.
- To add a vertex to a line or polygon: drag the small midpoint indicator that appears on a segment between two vertices — dragging it away from the segment inserts a new vertex there.
- To remove a vertex from a line or polygon: hold Alt and click the vertex.
- Click the button again to exit move mode.
How to download features?
Click the Download button download to open the format selector. Choose between GeoJSON and KML.
GeoJSON exports to capto_features.geojson. Compatible with QGIS, ArcGIS, Mapbox, and any GeoJSON-aware tool. Each feature includes its custom properties plus layerName and layerColor.
KML exports to capto_features.kml. Compatible with Google Earth, Google Maps, and GIS tools that support KML. Features are grouped into folders by layer, styled with the layer's color, and custom properties are included as ExtendedData.
Both formats include only features from visible layers. Hidden layers are excluded.
How to delete a feature?
- Click on the feature you want to delete. It will turn orange.
- Click the Delete feature button in the toolbar.
- Confirm the deletion in the dialog that appears. The feature will be immediately removed from the map and from storage.
- You can also press the Delete key on your keyboard after selecting a feature.
How to zoom to fit all features?
The Zoom Fit button zoom_out_map adjusts the map view to show all features from visible layers at once — useful after drawing many features or returning from a distant location.
- Click the zoom_out_map button in the toolbar.
- The map animates smoothly to frame all visible features.
- Features in hidden layers are not included in the fit.
- You can also zoom to a single layer using the zoom_out_map button in each layer row inside the Layers panel.
How to edit a feature?
- Click on the feature you want to edit. It will turn orange.
- Click the Edit button edit in the toolbar.
- A dialog appears pre-filled with the feature's current name, layer, and properties. You can change any of them — add, edit, or remove property rows the same way as when creating a feature.
- Click Save changes to confirm. If you changed the layer, the feature moves to the new layer instantly.
- If labels are enabled for that layer, the updated name appears on the map immediately.
How to use layers?
Layers let you organize features into named, color-coded groups. The layers panel also controls base map visibility and per-layer label display.
- Click the Layers button layers in the toolbar to open the layers panel.
- The Base map row at the top controls the OpenStreetMap tile visibility. Click visibility to hide it (useful for a clean export or dark background).
- The active layer (where new features will be placed) is highlighted in blue. Click any layer row to make it the active layer.
- Use the visibility button to show or hide a layer's features.
- Use the sell button to toggle feature name labels for that layer. The icon turns solid sell when labels are on. This setting is saved per layer.
- Use the zoom_out_map button to zoom the map to fit all features in that layer.
- Click the color circle to change a layer's color. All its features — points, lines, and polygons alike — update instantly.
- Use the checklist button to define that layer's property schema — a list of field names (e.g. "species", "height") that will come pre-filled whenever you add a feature to this layer. Type a name in a row to save it, click add to add another field, or close to remove one. This is just a starting point — features can still have extra fields beyond the schema. Don't add a field called "name" — every feature already has one built in (see "How to add custom properties to a feature?" above).
- Use the edit button to rename a layer inline.
- Use the delete button to delete a layer and all its features (cannot be undone).
- Click + Add layer at the bottom to create a new layer with a custom name and color.
How to add a point at my current location?
- Click the Add point at current location button my_location in the toolbar.
- If prompted, allow the browser to access your location.
- The map centers on your estimated location and shows a small round marker there, along with a dialog asking for a name, layer, and optional properties.
- Fill in the dialog and click Add feature to accept the location, or Cancel to discard it — either way, the round preview marker disappears once you decide.
If geolocation is denied or unavailable, the app will notify you with an error message. This tool always creates a point — for lines and polygons, use the draw tools above.