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/main/java/org/elasticsearch/xpack/vectortile/rest/VectorTileRequest.java
public static final int EXTENT = 4096;
        public static final boolean EXACT_BOUNDS = false;
        public static final int TRACK_TOTAL_HITS_UP_TO = DEFAULT_TRACK_TOTAL_HITS_UP_TO;
    }
    private static final ObjectParser<VectorTileRequest, RestRequest> PARSER;
    static {
        PARSER = new ObjectParser<>("vector-tile");
        PARSER.declareInt(VectorTileRequest::setSize, SearchSourceBuilder.SIZE_FIELD);
        PARSER.declareField(VectorTileRequest::setFieldAndFormats, (p) -> {
            List<FieldAndFormat> fetchFields = new ArrayList<>();
            while ((p.nextToken()) != XContentParser.Token.END_ARRAY) {
                fetchFields.add(FieldAndFormat.fromXContent(p));
            }
            return fetchFields;
        }, SearchSourceBuilder.FETCH_FIELDS_FIELD, ObjectParser.ValueType.OBJECT_ARRAY);
        PARSER.declareField(
            VectorTileRequest::setQueryBuilder,
            (CheckedFunction<XContentParser, QueryBuilder, IOException>) AbstractQueryBuilder::parseInnerQueryBuilder,
            SearchSourceBuilder.QUERY_FIELD,
            ObjectParser.ValueType.OBJECT
        );
        PARSER.declareField(
            VectorTileRequest::setRuntimeMappings,
            XContentParser::map,
            SearchSourceBuilder.RUNTIME_MAPPINGS_FIELD,
            ObjectParser.ValueType.OBJECT
        );
        PARSER.declareField(
            VectorTileRequest::setAggBuilder,
            AggregatorFactories::parseAggregators,