Geospatial queries basics in MongoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Find documents within a circle

Given a MongoDB collection places with documents containing a location field as GeoJSON points, what will be the output of this query?

db.places.find({ location: { $geoWithin: { $centerSphere: [[-73.97, 40.77], 0.0001] } } })

The query finds documents within a circle centered at longitude -73.97, latitude 40.77 with radius 0.0001 radians.

A Documents with locations roughly within 637 meters of the point (-73.97, 40.77)

B Documents with locations exactly at (-73.97, 40.77) only

C Documents with locations within 0.01 degrees of the point (-73.97, 40.77)

D Documents with locations anywhere in the collection

💡 Hint

Remember that $centerSphere uses radians for radius, not degrees or meters.

The $centerSphere operator defines a circle on the Earth's surface using radians. Radius 0.0001 radians corresponds to about 637 meters (0.0001 * Earth's radius ≈ 6371 km). So the query returns documents whose location is within that circle.

🧠 Conceptual

intermediate

Understanding 2dsphere index usage

Which statement about MongoDB's 2dsphere index is correct?

A It is used only for legacy coordinate pairs, not GeoJSON.

B It automatically converts all coordinates to degrees before indexing.

C It supports queries on GeoJSON objects and calculates distances on a spherical surface.

D It only supports flat 2D plane calculations and cannot handle GeoJSON points.

💡 Hint

Think about how Earth’s curvature affects distance calculations.

The 2dsphere index supports GeoJSON objects and performs calculations assuming a spherical Earth, which is important for accurate geospatial queries.

📝 Syntax

advanced

Identify the syntax error in a geospatial query

Which option contains a syntax error in the MongoDB geospatial query?

MongoDB

db.places.find({ location: { $near: { $geometry: { type: "Point", coordinates: [-73.97, 40.77] }, $maxDistance: 1000 } } })

A db.places.find({ location: { $near: { $geometry: { type: "Point", coordinates: [-73.97, 40.77] }, maxDistance: 1000 } } })

B db.places.find({ location: { $near: { $geometry: { type: "Point", coordinates: [-73.97, 40.77] }, $maxDistance: 1000 } } })

C db.places.find({ location: { $near: { $geometry: { type: "Point", coordinates: [40.77, -73.97] }, $maxDistance: 1000 } } })

D db.places.find({ location: { $nearSphere: { $geometry: { type: "Point", coordinates: [-73.97, 40.77] }, $maxDistance: 1000 } } })

💡 Hint

Check the spelling and syntax of the distance option inside $near.

In MongoDB geospatial queries, the distance option must be $maxDistance with a dollar sign. Option A uses maxDistance without the dollar sign, causing a syntax error.

❓ optimization

advanced

Optimizing geospatial queries with indexes

You have a collection restaurants with a location field storing GeoJSON points. Which index will optimize queries that find restaurants near a given point?

A { location: "2d" }

B { location: "2dsphere" }

C { location: "hashed" }

D { location: 1 }

💡 Hint

Consider the type of geospatial data stored and the query type.

The 2dsphere index supports GeoJSON points and spherical calculations, which are needed for near queries on Earth coordinates. The 2d index is for flat coordinate pairs and does not support GeoJSON.

🔧 Debug

expert

Why does this geospatial query return no results?

You run this query on a MongoDB collection parks with a location field indexed as 2dsphere:

db.parks.find({ location: { $geoWithin: { $box: [[-74, 40], [-73, 41]] } } })

But it returns no documents, even though you know some parks are inside that box. What is the most likely reason?

A The $geoWithin operator requires $centerSphere, not $box.

B The coordinates in $box are reversed; longitude and latitude are swapped.

C The collection does not have any documents with location fields.

D The $box operator only works with 2d indexes, not 2dsphere indexes.

💡 Hint

Check compatibility of operators with index types.

The $box operator works only with legacy 2d indexes and flat coordinate pairs. It is not supported with 2dsphere indexes, which require GeoJSON geometry operators like $geometry or $centerSphere.