Region / geo shape search with elasticsearch
On my previous article, I have demonstrated how to search for locations, which is basically points, given a region (in form of polygon) or central point. Now what if we have a bunch of regions and we want to query those regions, to answer the question of “given a point and a circle from that point, what are the regions that surround it?”.
1. Create index mapping
I will create similar index mapping, but this time, instead of using geo_point, since I would like to represent a region, I will have to use geo_shape type.
PUT ny-clusters-001
{
"mappings": {
"properties": {
"cluster": {"type": "geo_shape"},
"cluster_name": {"type": "text"}
}
}
}
2. Insert documents
Again I shall re-draw maps with those regions. Here, I will pick New York City Hall, and draw 3 regions in this custom map.
you can see there are 3 gray regions, that I have drawn. My maps feature has enabled us to download the regions as CSV, with well-known text (WKT) format. This WKT could be imported directly into elasticsearch! I will demonstrate the api calls to populate those regions as below.
POST ny-clusters-001/_doc
{
"cluster_name": "NY City Hall",
"cluster": "POLYGON ((-74.0080488 40.7120072, -74.0076089 40.7116819, -74.005608 40.7122105, -74.0051145 40.7123813, -74.0047819 40.7125521, -74.0042508 40.7131335, -74.0062947 40.7141257, -74.0080488 40.7120072))"
}
POST ny-clusters-001/_doc
{
"cluster_name": "NY City Hall Cluster 1",
"cluster": "POLYGON ((-74.0099852 40.712137, -74.0086549 40.7115352, -74.0063911 40.7141538, -74.0078931 40.7148532, -74.0099852 40.712137))"
}
POST ny-clusters-001/_doc
{
"cluster_name": "NY City Hall Cluster 2",
"cluster": "POLYGON ((-74.0048139 40.7124379, -74.0014129 40.7099168, -73.9983445 40.7132512, -74.0020995 40.715089, -74.0025072 40.7142921, -74.0033977 40.7136903, -74.0048139 40.7124379))"
}
3. Query by point and distance
Now I have my data, it’s time to query those region.
This first query will results in 2 regions: NY City Hall and NY City Hall Cluster 1, because those 2 regions are the only regions that could be intersected by “circle” within 71 meters from the query point. The query point and distance could be ilustrated as below.
The sample request to search is as follow.
GET ny-clusters-001/_search
{
"query": {
"geo_distance": {
"distance": "71m",
"cluster": {
"lat": 40.71182,
"lon": -74.00531
}
}
}
}
This will return all the data that I have, since I have expanded the query “circle” to include all of the regions. Now the query region will look like this.
And we will need to alter the geo_distance’s distance
GET ny-clusters-001/_search
{
"query": {
"geo_distance": {
"distance": "250m",
"cluster": {
"lat": 40.71182,
"lon": -74.00531
}
}
}
}
There you have it! I can now use this elasticsearch to query regions!
References
- https://www.elastic.co/guide/en/elasticsearch/reference/7.17/query-dsl-geo-distance-query.html
- https://en.wikipedia.org/wiki/Well-known_text_representation_of_geometry