Zoom in on Map Point with a Radius

My blog has moved to jimdehner.com 

Thank you for all the support over the past 2 years - I recently updated my blog to make it easier to read, improve the rendering of images and tie back to video presentations that are associated with the content - Check it out at  Jim's new blog  -   

"Zoom In" - to Points on Map

 

Recently there have several Forum post asking how to find all the points that are within a radius of a point and to be able to "zoom in" on the map – something like “I want to identify client locations are within 20 miles of each of our 5 office locations of out plant locations”  - 

 
Not an un-common question – and very solvable with Tableau - but being able to "Zoom in" requires a bit of a hack 

Like a lot of solutions in Tableau, you need to think backwards . First we  need to determine the distance from each office to each client location in the data – Then apply a filter that eliminates the points a greater distance away.  Not difficult but a lot of data

Step 1 – Shape the Data

You need to have the longitude and latitude of each office and each client location – sorry you won’t be able to use the Tableau generated longs and lats in calculations, so they need to be loaded with the data - keep the files separate - one for the office and one for the client locations.

To get the solution we need to determine the distance from each office location to every client site and will require connecting the files together with a Cartesian join

 

The join expands the data set with a separate row for each client location / office site combination

Step 2 – Determine the distance from the office to each client



I’ve used an LOD that looks at each Office location and determines the distance to every Client location 

{ FIXED [Client Loc ID],[Office Loc ID]   :avg(3959 * ACOS(

 SIN(RADIANS([Client Lat])) * SIN(RADIANS(([Office Lat]))) +

 COS(RADIANS([Client Lat])) * COS(RADIANS(([Office Lat]))) *

 COS(RADIANS(([Office Long]))-RADIANS([Client Long])))  )}

Note: I used the explicit formula rather than the Distance spatial function added in version 2019 - 

The fixed LOD can be read in words as : for each combination of the office and client location calculate the “as the crow files distance” using a complex trig formula --  

Step 3 Create a Parameter to enter the radius and a filter based on the parameter

I used a floating point parameter and used a range up to 60 miles with steps of 10 miles – you can use whatever fits your analysis

 
Then add a simple filter that limits the distance between the city center to the value in the parameter – place it on the filter shelf and set to TRUE

 [Distance Office to Client]<= [Enter Radius]

Step 4 - Create the Map

The Viz is a dual axis map - one layer contains the Client locations the other the Office sites
Filters are added on the Office site location and the Boolean distance filter.  I made the Office locations stars - could be any shape - and I use the State dimension to vary the color of the client locations

Convert the map to Dual Axis then go to the Map button on the top ribbon, open and select Map Layers - in the box that opens you will be able to select the style and the layers you want to see

Step 5 - the Zoom feature

Finally the Zoom feature is controlled by the radius - the smaller the radius the more the user "Zooms" in and conversely larger radii will "Zoom Out"  BUT you MUST UNPIN the map and UNSELECT the Pan and Zoom on the Map Options to avoid the map being locked at a zoom level and office location

Bring the map and filter and parameter to a dashboard and annotate as needed

I have a similar map on my Tableau Public site at  
https://public.tableau.com/profile/jim.dehner#!/vizhome/Findclientswithinradius_v10_5/Interactivemap

Feel free to download it (or any other file on the site) to use as a model 

Jim