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Define Location Precision for a 2d Index

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  • About this Task
  • Before You Begin
  • Procedure
  • Next Steps
  • Learn More

In a 2d index, location precision is defined by the size in bits of the geohash values used to store the indexed data. By default, 2d indexes use 26 bits of precision, which is equivalent to approximately two feet (60 centimeters).

Location precision affects performance for insert and read operations.

To change the default precision, specify a bits value when you create the 2d index. You can specify a bits value between 1 and 32, inclusive.

db.<collection>.createIndex(
   { <location field>: "2d" },
   { bits: <bit precision> }
)

About this Task

Location precision affects query performance:

  • Lower precision improves performance for insert and update operations, and uses less storage.

  • Higher precision improves performance for read operations because queries scan smaller portions of the index to return results.

Location precision does not affect query accuracy. Grid coordinates are always used in the final query processing.

Before You Begin

Create the contacts collection:

db.contacts.insertMany( [
   {
      name: "Evander Otylia",
      phone: "202-555-0193",
      address: [ 55.5, 42.3 ]
   },
   {
      name: "Georgine Lestaw",
      phone: "714-555-0107",
      address: [ -74, 44.74 ]
   }
] )

The address field contains legacy coordinate pairs.

Procedure

Create a 2d index on the address field. Specify a location precision of 32 bits:

db.contacts.createIndex(
   { address: "2d" },
   { bits: 32 }
)

Next Steps

You can use the 2d index to perform calculations on location data, such as proximity queries.

Learn More

← Create a 2d Index
Define Location Range for a 2d Index →

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