Random geographic coordinates (on land, avoid ocean)

Question

Any clever ideas on how to generate random coordinates (latitude / longitude) of places on Earth? Latitude / Longitude. Precision to 5 points and avoid bodies of water. <

Answer 1

This has being asked a long time ago and I now have the similar need. There are two possibilities I am looking into:

1. Define the surface ranges for the random generator.

Here it's important to identify the level of precision you are going for. The easiest way would be to have a very relaxed and approximate approach. In this case you can divide the world map into "boxes":

Each box has it's own range of lat lon. Then you first randomise to get a random box, then you randomise to get a random lat and random long within the boundaries of that box.

Precisions is of course not the best at all here... Though it depends:) If you do your homework well and define a lot of boxes covering most complex surface shapes - you might be quite ok with the precision.

2. List item

Some API to return continent name from coordinates OR address OR country OR district = something that WATER doesn't have. Google Maps API's can help here. I didn't research this one deeper, but I think it's possible, though you will have to run the check on each generated pair of coordinates and rerun IF it's wrong. So you can get a bit stuck if random generator keeps throwing you in the ocean.

Also - some water does belong to countries, districts...so yeah, not very precise.

For my needs - I am going with "boxes" because I also want to control exact areas from which the random coordinates are taken and don't mind if it lands on a lake or river, just not open ocean:)

Answer 2

Supplementary to what bsimic said about digging into GeoNames' Webservices, here is a shortcut:
they have a dedicated WebService for requesting an ocean name.

(I am aware the of OP's constraint to not using public web services due to the amount of requests. Nevertheless I stumbled upon this with the same basic question and consider this helpful.)

Go to http://www.geonames.org/export/web-services.html#astergdem and have a look at "Ocean / reverse geocoding". It is available as XML and JSON. Create a free user account to prevent daily limits on the demo account.

Request example on ocean area (Baltic Sea, JSON-URL):

http://api.geonames.org/oceanJSON?lat=54.049889&lng=10.851388&username=demo

results in

{
  "ocean": {
    "distance": "0",
    "name": "Baltic Sea"
  }
}

while some coordinates on land result in

{
  "status": {
    "message": "we are afraid we could not find an ocean for latitude and longitude :53.0,9.0",
    "value": 15
  }
}

Answer 3

Assuming Atlantis isn't in the database, you could randomly select cities. This also provides a more realistic distribution of points if you intend to mimic human activity: https://simplemaps.com/data/world-cities

There's only 7,300 cities in the free version.

Answer 4

To get a nice even distribution over latitudes and longitudes you should do something like this to get the right angles:

double longitude = Math.random() * Math.PI * 2;
double latitude = Math.acos(Math.random() * 2 - 1);

As for avoiding bodies of water, do you have the data for where water is already? Well, just resample until you get a hit! If you don't have this data already then it seems some other people have some better suggestions than I would for that...

Hope this helps, cheers.

Answer 5

As a plan B, maybe you can pick a random country and then pick a random coordinate inside of this country. To be fair when picking a country, you can use its area as weight.

Answer 6

There is a library here and you can use its .random() method to get a random coordinate. Then you can use GeoNames WebServices to determine whether it is on land or not. They have a list of webservices and you'll just have to use the right one. GeoNames is free and reliable.