6.3. Index Basics

GeoMesa will create various indices for a given SimpleFeatureType schema (see Index Overview). This allows us to answer a variety of queries in a optimized manner. GeoMesa will make a best effort to determine the attributes used for indexing. The attributes to use can also be specified as part of the SimpleFeatureType.

6.3.1. Spatial Index (Z2/XZ2)

If the SimpleFeatureType has a Geometry-type attribute (Point, LineString, Polygon, etc), GeoMesa will create a spatial index on that attribute. If there is more than one Geometry-type attribute, the default one will be used. The default geometry is generally specified with a * prefix in the SimpleFeatureType string, and is the one returned by SimpleFeatureType.getGeometryDescriptor.

6.3.2. Spatio-temporal Index (Z3/XZ3)

If the SimpleFeatureType has both a Geometry-type attribute and a Date attribute, GeoMesa will create a spatio-temporal index on those attributes. The Geometry-type attribute used is the same as for the spatial index, above. The Date attribute selected will be the first one declared, or can be set explicitly. See Setting the Indexed Date Attribute for details on setting the indexed date.

6.3.3. ID Index

GeoMesa will always create an ID index on SimpleFeature.getID().

6.3.4. Attribute Index

Some queries are slow to answer using the default indices. For example, with twitter data you might want to return all tweets for a given user. To speed up this type of query, any attribute in your simple feature type may be indexed individually.

To index an attribute, add an index key to the attribute descriptor user data with a value of true.

Note

Accumulo data stores have an additional option to create reduced ‘join’ attribute indices, which can save space. See Accumulo Attribute Indices for details.

SimpleFeatureType sft = ...
sft.getDescriptor("name").getUserData().put("index", "true");

If you are using the GeoMesa SftBuilder, you may call the overloaded attribute methods:

// scala example
import org.locationtech.geomesa.utils.geotools.SftBuilder.SftBuilder

val sft = new SftBuilder()
    .stringType("name", Opts(index = true)
    .date("dtg")
    .geometry("geom", default = true)
    .build("mySft")

Setting the user data can be done in multiple ways. See Setting Schema Options for more details.

To prioritize certain attributes over others, see Cardinality Hints.