CODEWITHSUNDEEP
gisopenstreetmapopenlayers-3
ElKroketto
ElKroketto

Reputation: 23

Discrepancy between OpenLayers 3 OSM-tiles and Natural Earth

I have extracted a sample geometry dataset from the 10m coastline collection (Link by Natural Earth) using geoTools. Then I added it as LineString-Vector in Open Layers 3 - The results are not too bad, but there is quite a discrepancy between the OpenStreetMap tiles and the drawn vector. Take a look at the resulting map in this JSFiddle

var coords = [
    [14.027842644000089, 68.26264069200005],[13.99350019600007, 68.25787995000007], ...
];
var lineString = new ol.geom.LineString(coords);
lineString.transform('EPSG:4326', 'EPSG:3857');

Any ideas what is causing this difference? If the error is coming from the different datasets, which one is the more accurate?

Thanks a lot in advance and best regards Elias

Upvotes: 2

Views: 352

Answers (2)

Andrew Reid
Andrew Reid

Reputation: 38161

The coastline layer does not appear to be skewed one direction or another, the skew should be fairly consistent across a region if it is an issue of accuracy.

The 10m in the name refers to a 1 to 10 000 000 scale, this would explain why the shape appears to be imprecise. The general shape is right, the detail is missing. Even though it is the highest quality from Natural Earth, the 2.93 megabytes the world coastline data fills is insufficient to detail specific smaller areas. Given the island of Vestvågøya (the island shown in question's fiddle) is roughtly 400 square kilometers, you should be looking for data that is less than 1:1 000 000 (off the top of my head, I usually work with 1:250 000 or 1:50 000 data for areas that size and smaller (and there is a 25x difference in detail between those two, not to mention 1:10 000 000)).

You may find greater success in using Norway specific geographic data to get more specific detail of your target area.

Edit: If you are looking at coastline data worldwide (comment below), you might want to take a look at the Open Street Map coastline data (here). This should also have the advantage of lining up with Open Street Map tiles. It is much more detailed, but that detail comes at the cost of size, over 600mb unpacked. It is a line geometry, the land data (polygons, should contain the same detail) might be better in some scenarios as it could allow you to screen out islets under a certain size. Compared below, open street map data and natural earth data (of Vestvågøya):

enter image description here

Upvotes: 4

Sumanth Shastry
Sumanth Shastry

Reputation: 1159

Go through the isses of 10M coastline

http://www.naturalearthdata.com/downloads/10m-physical-vectors/10m-coastline/

which specifies there is suspect accuracy for certain parts of the world, including northern Russia. Since the location you are trying is close to Northern Russia there might be some discrepancies. Not 100% sure.

Upvotes: 1

Related Questions