Geo-proximity with sorted sets in Redis - Step-by-Step Execution

Concept Flow - Geo-proximity with sorted sets

Add locations with GEOADD

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Store locations in sorted set with geo info

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Use GEORADIUS or GEOSEARCH to find nearby locations

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Sort results by distance

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Return locations with distances

Locations are added to a sorted set with geo info, then queried by radius to find and sort nearby places.

Execution Sample

Redis

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

Add two places and find all within 200 km of point (15,37), sorted by distance.

Execution Table

Step	Command	Action	Result	Notes
1	GEOADD places 13.361389 38.115556 "Palermo"	Add Palermo location	Added 1	Palermo stored in 'places' sorted set
2	GEOADD places 15.087269 37.502669 "Catania"	Add Catania location	Added 1	Catania stored in 'places' sorted set
3	GEORADIUS places 15 37 200 km WITHDIST ASC	Find locations within 200 km of (15,37)	[["Catania", 56.4413], ["Palermo", 190.4424]]	Results sorted by distance ascending
4	End	No more commands	Query complete	Execution stops after query

💡 All commands executed; GEORADIUS returns sorted nearby locations within radius.

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
places	empty	[Palermo]	[Palermo, Catania]	[Palermo, Catania]	[Palermo, Catania]
query_result	none	none	none	[[Catania, 56.4413], [Palermo, 190.4424]]	[[Catania, 56.4413], [Palermo, 190.4424]]

Key Moments - 2 Insights

Why does GEORADIUS return Catania before Palermo even though Palermo was added first?

GEORADIUS sorts results by distance when ASC is specified, so Catania is closer to (15,37) than Palermo, shown in execution_table row 3.

What does the WITHDIST option do in the GEORADIUS command?

WITHDIST makes GEORADIUS return the distance of each location from the center point, as seen in the result distances in execution_table row 3.

Visual Quiz - 3 Questions

Look at the execution_table row 3, what is the distance from (15,37) to Palermo?

A 15 km

B 56.4413 km

C 190.4424 km

D 37 km

💡 Hint

Check the distances listed in the GEORADIUS result in execution_table row 3.

At which step is the second location added to the sorted set?

A Step 2

B Step 3

C Step 1

D Step 4

💡 Hint

Look at the commands in execution_table rows 1 and 2.

If the radius in GEORADIUS was changed to 50 km, what would happen to the query_result?

A Both Palermo and Catania would be returned

B No locations would be returned

C Only Palermo would be returned

D Only Catania would be returned

💡 Hint

Refer to the distances in execution_table row 3 and compare with 50 km radius.

Concept Snapshot

GEOADD key longitude latitude member - adds geo location to sorted set
GEORADIUS key longitude latitude radius m|km WITHDIST ASC|DESC - finds nearby locations sorted by distance
WITHDIST returns distance with each location
Results sorted by distance if ASC or DESC specified
Use for geo proximity queries in Redis

Full Transcript

This visual execution shows how Redis stores geo locations in a sorted set using GEOADD. Two locations, Palermo and Catania, are added with their longitude and latitude. Then GEORADIUS queries locations within 200 km of point (15,37), returning Catania and Palermo sorted by distance ascending. The WITHDIST option includes the distance in the results. The execution table tracks each command and result, and the variable tracker shows how the 'places' set and query results change. Key moments clarify why sorting happens by distance and what WITHDIST does. The quiz tests understanding of distances, command steps, and radius effects. This helps beginners see step-by-step how geo proximity queries work with Redis sorted sets.

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