This isn't about where to put the id of a piece of unique content in URLs, but more about densely packing the URL (or, does it just not matter).Take for example, a hypothetical post in a blog:http://tempuri.org/123456789/seo-friendly-titleThe ID that uniquely identifies this is 123456789.  This corresponds to a look-up and is the direct key in the underlying data store.However, I could encode that in say, hexadecimal, like so:http://tempuri.org/75bcd15/seo-friendly-titleAnd that would be shorter.One could take it even further and have more compact encodings; since URLs are case sensitive, one could imagine an encoding that uses numbers, lowercase and uppercase letters, for a base of 62 (26 upper case + 26 lower case + 10 digits):0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyzFor a resulting URL of:http://tempuri.org/8M0kX/seo-friendly-titleThe question is, does densely packing the ID of the content (the requirement is that an ID is mandatory for look-ups) have a negative impact on SEO (and dare I ask, might it have any positive impact), or is it just not worth the time?Note that this is not for a URL shortening service, so saving space in the URL for browser limitation purposes is not an issue.
Is SEO affected negatively by having densely encoded identifiers of content in URLs?
seo;url
Generally speaking, it's not going to make a difference one way or another. The unique IDs won't affect your rankings directly unless you're actually trying to rank for search terms containing those IDs (you aren't). So their form isn't important to the search engines.Where they can affect SEO is edge cases where you have a very long URL. Obviously if the search engines have a limit to how far they will read, and find the keywords in, a URL and you exceed it the keywords at the end of the URL will be invisible to them. Or less advanced search engines may cause the page not to be indexed at all. In these cases a shorter identifier would be a positive thing. But your URL would need to be very long for this really to be a factor (and well written software can easily prevent this from occurring in the first place).