Vector tiles buffer is used to include data that is just outside of the tile. This data is used to prevent border effects when rendering the geometries. It is currently [hardcoded to 5 pixels](https://github.com/elastic/elasticsearch/blob/de2781f98696c1e6cfad2b5bf46fe752a5e3edbb/x-pack/plugin/vector-tile/src/main/java/org/elasticsearch/xpack/vectortile/feature/FeatureFactory.java#L63) but it should probably need to be user configurable by adding a new property on the vector tiles API which can change the value.




x-pack/plugin/vector-tile/src/test/java/org/elasticsearch/xpack/vectortile/rest/VectorTileRequestTests.java
consumer.accept(builder);
        builder.endObject();
        final FakeRestRequest request = requestBuilder.withContent(BytesReference.bytes(builder), builder.contentType()).build();
        final VectorTileRequest vectorTileRequest = VectorTileRequest.parseRestRequest(request);
        assertThat(vectorTileRequest.getIndexes(), Matchers.equalTo(new String[] { index }));
        assertThat(vectorTileRequest.getField(), Matchers.equalTo(field));
        assertThat(vectorTileRequest.getZ(), Matchers.equalTo(z));
        assertThat(vectorTileRequest.getX(), Matchers.equalTo(x));
        assertThat(vectorTileRequest.getY(), Matchers.equalTo(y));
        asserter.accept(vectorTileRequest);
    }
    private FakeRestRequest.Builder getBasicRequestBuilder(String index, String field, int z, int x, int y) {
        return new FakeRestRequest.Builder(xContentRegistry()).withMethod(RestRequest.Method.GET)
            .withParams(
                Map.of(
                    VectorTileRequest.INDEX_PARAM,
                    index,
                    VectorTileRequest.FIELD_PARAM,
                    field,
                    VectorTileRequest.Z_PARAM,
                    "" + z,
                    VectorTileRequest.X_PARAM,
                    "" + x,
                    VectorTileRequest.Y_PARAM,
                    "" + y
                )
            );
    }
}