Geo-proximity with sorted sets in Redis - Mini Project: Build & Apply

Geo-proximity with sorted sets

📖 Scenario: You are building a simple location-based service that stores places with their geographic coordinates. You want to find places near a specific location.

🎯 Goal: Create a Redis sorted set to store places with their longitude and latitude. Then, configure a radius distance. Next, query the sorted set to find places within that radius sorted by distance. Finally, complete the setup to return the results with distances.

📋 What You'll Learn

Create a sorted set called places with three places and their longitude and latitude using GEOADD.

Create a variable radius set to 10 kilometers.

Use GEORADIUS command on places with center longitude 13.361389 and latitude 38.115556, radius radius, unit km, and sort results by distance ascending.

Add the option to return distances with the results.

💡 Why This Matters

🌍 Real World

Location-based services like finding nearby restaurants, stores, or landmarks use geo-proximity queries to provide relevant results to users.

💼 Career

Understanding Redis geo commands is useful for backend developers working on location-aware applications, improving user experience with fast and efficient geographic queries.

1

Create the sorted set with places

Use the GEOADD command to add these three places to a sorted set called places with their exact longitude and latitude: Palermo (13.361389, 38.115556), Catania (15.087269, 37.502669), and Messina (15.550000, 38.193000).

Redis

# Use GEOADD to add Palermo, Catania, and Messina to 'places'
# Your code here

Hint

Use GEOADD places longitude latitude member format for each place.

2

Set the radius variable

Create a variable called radius and set it to 10 to represent 10 kilometers.

Redis

GEOADD places 13.361389 38.115556 Palermo 15.087269 37.502669 Catania 15.550000 38.193000 Messina
# Set radius variable to 10
# Your code here

Hint

Use SET radius 10 to create the variable.

3

Query places within radius sorted by distance

Use the GEORADIUS command on places with center longitude 13.361389 and latitude 38.115556, radius radius, unit km, and sort the results by distance ascending using ASC.

Redis

GEOADD places 13.361389 38.115556 Palermo 15.087269 37.502669 Catania 15.550000 38.193000 Messina
SET radius 10
# Use GEORADIUS to find places within radius sorted by distance ascending
# Your code here

Hint

Use GEORADIUS places longitude latitude radius km ASC to get sorted results.

4

Return distances with the results

Add the WITHDIST option to the GEORADIUS command to return the distances along with the place names.

Redis

GEOADD places 13.361389 38.115556 Palermo 15.087269 37.502669 Catania 15.550000 38.193000 Messina
SET radius 10
GEORADIUS places 13.361389 38.115556 10 km ASC
# Add WITHDIST option to return distances
# Your code here

Hint

Add WITHDIST after ASC in the GEORADIUS command.

Practice

1. What does the Redis command GEOADD do in the context of geo-proximity with sorted sets?

easy

A. Returns the distance between two members

B. Finds all members within a radius from a point

C. Removes a location from the sorted set

D. Adds geographic locations (longitude, latitude) to a sorted set

Solution

1. Step 1: Understand the purpose of GEOADD

   The GEOADD command stores geographic coordinates (longitude and latitude) associated with a member in a sorted set.

2. Step 2: Differentiate GEOADD from other geo commands

   Commands like GEORADIUS find nearby members, while GEOADD adds new locations.

3. Final Answer:

   Adds geographic locations (longitude, latitude) to a sorted set -> Option D

4. Quick Check:

   GEOADD = Add locations [OK]

Hint: GEOADD always adds locations with coordinates [OK]

Common Mistakes:

• Confusing GEOADD with GEORADIUS
• Thinking GEOADD removes locations
• Assuming GEOADD returns distances

2. Which of the following is the correct syntax to find members within 5 kilometers of longitude 13.361389 and latitude 38.115556 using Redis GEO commands?

easy

A. GEOADD locations 13.361389 38.115556 5 km

B. GEODIST locations 13.361389 38.115556 5 km

C. GEORADIUS locations 13.361389 38.115556 5 km

D. GEORADIUSBYMEMBER locations 13.361389 38.115556 5 km

Solution

1. Step 1: Identify the command to find nearby members

   GEORADIUS is used to find members within a radius from given longitude and latitude.

2. Step 2: Check syntax correctness

   GEORADIUS locations 13.361389 38.115556 5 km correctly specifies key, longitude, latitude, radius, and unit.

3. Final Answer:

   GEORADIUS locations 13.361389 38.115556 5 km -> Option C

4. Quick Check:

   GEORADIUS + lon lat + radius + unit = correct syntax [OK]

Hint: Use GEORADIUS with lon lat radius unit for proximity search [OK]

Common Mistakes:

• Using GEOADD instead of GEORADIUS for searching
• Mixing GEORADIUSBYMEMBER syntax with coordinates
• Using GEODIST which calculates distance, not radius search

3. Given the following Redis commands executed in order:

GEOADD cities 13.361389 38.115556 Palermo
GEOADD cities 15.087269 37.502669 Catania
GEORADIUS cities 15 37 200 km WITHDIST ASC

What will be the output?

medium

A. [["Palermo", "56.4413"], ["Catania", "190.4424"]]

B. [["Catania", "56.4413"], ["Palermo", "190.4424"]]

C. ["Palermo", "Catania"]

D. Syntax error

Solution

1. Step 1: Add two cities with their coordinates

   Palermo and Catania are added with their longitude and latitude to the 'cities' key.

2. Step 2: Use GEORADIUS to find cities within 200 km of (15, 37) sorted by distance ascending

   Catania is closer (~56.44 km), Palermo is farther (~190.44 km), so output lists Catania first with distances.

3. Final Answer:

   [["Catania", "56.4413"], ["Palermo", "190.4424"]] -> Option B

4. Quick Check:

   GEORADIUS WITHDIST ASC sorts by nearest first [OK]

Hint: WITHDIST returns distances; ASC sorts nearest first [OK]

Common Mistakes:

• Confusing order of results when using ASC
• Ignoring WITHDIST option for distances
• Swapping longitude and latitude values

4. You run the command GEORADIUS cities 15 37 100 km WITHDIST but get no results, even though you know cities exist nearby. What is the most likely cause?

medium

A. The key 'cities' does not exist or is empty

B. The longitude and latitude are swapped

C. The radius is too small to include any city

D. WITHDIST option is not supported

Solution

1. Step 1: Check if the key exists and has data

   If the 'cities' key does not exist or is empty, GEORADIUS returns no results regardless of radius.

2. Step 2: Consider other causes

   Radius 100 km is reasonable, WITHDIST is supported, and longitude/latitude order is correct, so these are less likely.

3. Final Answer:

   The key 'cities' does not exist or is empty -> Option A

4. Quick Check:

   Empty key = no results [OK]

Hint: Check if key exists before searching [OK]

Common Mistakes:

• Assuming WITHDIST causes errors
• Swapping lat/lon but still expecting results
• Using too small radius without verifying data

5. You want to find all locations within 10 miles of 'Denver' stored in a Redis sorted set 'places'. Which command correctly finds these locations using the member name 'Denver' as center and returns results sorted from nearest to farthest?

hard

A. GEORADIUSBYMEMBER places Denver 10 mi WITHDIST ASC

B. GEORADIUS places Denver 10 mi WITHDIST ASC

C. GEORADIUSBYMEMBER places Denver 10 mi WITHDIST DESC

D. GEODIST places Denver 10 mi WITHDIST ASC

Solution

1. Step 1: Use GEORADIUSBYMEMBER to search by member name

   GEORADIUSBYMEMBER finds locations near a member's coordinates, here 'Denver'.

2. Step 2: Specify radius and unit, and sort ascending by distance

   10 miles radius with WITHDIST ASC returns nearby locations sorted nearest first.

3. Final Answer:

   GEORADIUSBYMEMBER places Denver 10 mi WITHDIST ASC -> Option A

4. Quick Check:

   GEORADIUSBYMEMBER + WITHDIST ASC = nearest first [OK]

Hint: Use GEORADIUSBYMEMBER for member-centered radius search [OK]

Common Mistakes:

• Using GEORADIUS with member name instead of coordinates
• Sorting DESC instead of ASC for nearest first
• Using GEODIST which returns distance between two members only