How to group nearby latitude and longitude locations stored in SQL

Question

Im trying to analyse data from cycle accidents in the UK to find statistical black spots. Here is the example of the data from another website. http://www.cycleinjury.co.uk

Answer 1

First, your example is quite misleading. You have two different sets of data, and you don't control the data. If it appears in a chain, then you will get a chain out.

This problem is not exactly suitable for a database. You'll have to write code or find a package that implements this algorithm on your platform.

There are many different clustering algorithms. One, k-means, is an iterative algorithm where you look for a fixed number of clusters. k-means requires a few complete scans of the data, and voila, you have your clusters. Indexes are not particularly helpful.

Another, which is usually appropriate on slightly smaller data sets, is hierarchical clustering -- you put the two closest things together, and then build the clusters. An index might be helpful here.

I recommend though that you peruse a site such as kdnuggets in order to see what software -- free and otherwise -- is available.