Geometry Viewer

How the Geometry Viewer works, and what it assumes

The input format is decided by its first character: a brace or a bracket means GeoJSON and anything else means WKT. Whichever it is, the geometry is read into one internal representation, drawn, and written back out in the format you choose, so the viewer doubles as a converter in either direction.

The picture is a plot, not a map. There is no basemap and no tile request, which is deliberate: fetching tiles would send the location of whatever you paste to a third-party server, and for a client's site boundary or an asset position that is exactly the disclosure this section is built to avoid. Instead the geometry is drawn as SVG on a labelled coordinate grid whose spacing adjusts to the extent, so the numbers stay readable whether you are looking at a continent or a building.

Coordinates inside the longitude and latitude range are treated as geographic degrees and the horizontal scale is multiplied by the cosine of the mean latitude, which keeps proportions roughly right — without it, a shape in Scandinavia would be drawn about twice as wide as it is. Coordinates outside that range are plotted one to one as projected units, with no earth model assumed and none claimed. Polygons are filled with the even-odd rule, so a hole is drawn as a hole.

Using the Geometry Viewer

• Seeing at a glance whether a geometry from a database is the shape you expected before writing any code.
• Spotting a self-intersecting or inside-out polygon, which is obvious in a picture and invisible in coordinates.
• Checking that a hole in a polygon really is inside its shell rather than beside it.
• Confirming that a geometry whose numbers look odd is projected rather than geographic.

A worked example

Pasting a polygon with a hole:

POLYGON ((-0.1757 51.5025, -0.1501 51.5025, -0.1501 51.5128, -0.1757 51.5128, -0.1757 51.5025),
         (-0.1700 51.5060, -0.1600 51.5060, -0.1600 51.5100, -0.1700 51.5100, -0.1700 51.5060))

draws a rectangle with a rectangular gap in it, and reports:

Geometry            Polygon
Positions           10
South-west corner   -0.1757, 51.5025
North-east corner   -0.1501, 51.5128
Coordinates read as Geographic degrees

If the hole were drawn outside its shell, the picture would show two separate rectangles rather than one with a gap — which is instantly obvious here and invisible in the coordinates.

Where this comes up in GIS work

1. Paste WKT or GeoJSON into the input box, open a file, or select Load example. The format is detected automatically.
2. Choose whether the converted output should be GeoJSON or WKT.
3. Select Draw geometry, or press Ctrl + Enter (Cmd + Enter on a Mac).
4. Move the pointer over the plot to read off coordinates, and check the extent in the summary below it.
5. Copy or download the converted geometry, or select Clear to start again.

When the output looks wrong

The plot shows a single point when the geometry should be a shape

Every position in the geometry is the same, or the shape is far smaller than its coordinates suggest. Check the extent in the summary: if the corners are identical, the input really is one repeated position.

The geometry is drawn but has no basemap behind it

That is deliberate. Drawing a basemap means requesting map tiles from a third-party server, which would send the position of your data off this page. The plot is a coordinate grid instead, and nothing about your geometry leaves the browser.

Only the extent is shown, and the shape is not drawn

The geometry has more positions than the preview draws, which is capped so the page stays responsive. The extent, the position count and the conversion are all still computed from the whole geometry.

A shape near the poles looks stretched

Longitude degrees get shorter towards the poles, and the plot corrects for that using the mean latitude of the extent. Over a very tall extent one correction cannot fit the whole shape, so some distortion remains. A projected CRS is the proper fix.

Questions about the Geometry Viewer