It's nice to see there is at least something out there.  However both articles lack the necessary details about the work that was done to lend them credibility in my eyes. The first one is just a graph. There's several flaws.

The first one  I already mentioned but I'll discount it since there's no way around it. And that is, there could be a gazillion reasons why the rankings of those businesses went up that have nothing to do with making the citations more consistent.  I don't see any major algo updates during those periods though so that's good - so I'll give the benefit of the non-doubt here.  And I'll have to also go on a limb that there were no significant changes in the backlink profile and the website content of the majority of the properties used in these assessments - realistically, there probably was, but let's disregard it for argument sake.

Here's the missing piece - what types of NAP changes were made?  Specifically, I'd want to know what percentage of the NAPs where the city was changed, were they changed to a more densely populated area which naturally will get more 3-pack/map user impressions?

I'd say without someone like the new Matt Cuts confirming it's a significant ranking factor, it's still a mystery.  Those two reports of course were put out by companies that sell Local SEO services. (But who else would take the time to do them? LOL)

I think the bottom line is improving the consistency of your NAPs can only help your business.  But I think claims about it having a significant effect on organic rankings are still far from proven.

I've probably read the same "countless articles" but none of them even referenced any anecdotal evidence, let along a careful study.  I agree the study would be difficult because in the time between correcting the NAPs and the search engine picking up the corrections everywhere, there could be other factors that affect your ranking.  But if you are doing SEO for 100 local businesses, then you can pretty much determine with some degree of certainty whether it's essentially a myth or not.

So a "published study" to me might be someone like Brighlocal, say... We took 20 local business clients with NAP inconsistencies and monitored their rankings for two weeks on a daily basis and took the 10 of those 20 with the least variation in daily rankings and submitted corrections to their NAPs at the same time using the same method.  We performed no other on-page or off-page SEO for the next x weeks.  At the end of the "study" the rankings of the 10 businesses changed as follows....

Now of course there's still going to be external factors that can affect the ranking but  over time if you looked at similar data for more and more businesses you could be able to present fairly clear data that it makes a difference.

I've been doing Internet Marketing for almost 20 years and over that length of time you gain increased wisdom and gut instinct on things.  I'm not saying I can prove the NAP corrections make no significant difference in your ranking, but from all the articles I've read, the claims sure seem a bit fishy.  I've seen this before in other industries.  The presentation of misinformation, that on the surface makes sense, but really is just designed to make people think they need a product or service. That's the downside of the Internet, anyone can make any claim without basing it in actual fact.  Gee, the term "fake news" comes to mind.

Maybe if you could point to one of the countless articles written by someone very well respected in the industry I can pose the question "Specifically how were you able to determine that?"

Actually here's an article I ran across recently. Not sure how I stumbled on it and definitely wouldn't consider the author a widely respected publisher.  But he says:

https://www.stlouisdigitalmedia.com/blog/local-seo/what-is-nap-consistency/

"when search engines are crawling the web they can – and will – notice even the slightest variations in a business name, address, phone number, and/or website address. These variations can hinder a search engine’s confidence."

Okay, the first thing that popped into my head when I read this is "what specifically are you referring to regarding _confidence_ and how does that affect my organic ranking if the address and phone are correct but vary slightly from my other listings?"

Or, tell me why this matters so much and how you determined this?  Oh, you offer Local Search Marketing Services! Great! I can pay you to help me avoid the issues you are eluding to!

My gut is telling me using general descriptions like "hinder a search engine's confidence" means this author either is basically regurgitating something he heard elsewhere, also with no detailed justification, or is just making stuff up for the purpose of generating business.

Is everybody so sure the Emperor is actually wearing clothes?

Is the effect of NAP inconsistency on search rankings basically a myth to justify business citation management services? I've been doing SEO for over 10 years but only recently started doing local businesses. I have yet to find any sort of published study that clearly shows a significant ranking effect by correcting an inconsistent NAP on any business directory site other than Google and Bing Business Listings. In fact, the publishers of any such articles claiming NAP inconsistency has a significant negative SEO effect are almost always businesses or people that are charging for such services. Gee, could they be a little biased?

Obviously if you have an incorrect address that is far from the actual address, correcting it will help your ranking (think 3-pack) in the area close to your business but that's not really the type of ranking effect I'm talking about here.  I'm talking about a missing suite #, or an old address that is 1/2 block away from the new address but still the same phone number, or identical address but different phone (a toll free versus a local number). That kind of stuff.

Of course you don't want to have an incorrect address or non-working phone number on places like Superpages, Yelp, Yellowpages, etc, but does anyone know of any place I can find good factual proof that having inconsistent NAPs on these sites has any significant effect on rankings? I'm sure some of the big SEO companies have the data to determine the effect. Or is this more of a "tin foil hat" / herd / OCD mentality on this subject that no one can prove (or disprove?)

As usual with most discussion regarding sitemap, you will see 99% of people recommending them provide not concrete, fact based reason as to any actual benefit it provides.

• It provides no SEO advantage

• The reason that it's useful to users is like saying my primary navigation system and search function is too difficult to use.

• If you have a large website with lots of deep, frequently changing content, Google will recognize this and increase the crawl frequency and depth.

Sitemaps in my opinion or for the "tin foil hat" crowd.

But.. conversely, they don't hurt either.  If you have a plugin or script that automatically runs over and over to update it for you, then one could legitimately say "Why not?"

There are some obscure reasons one might use - like adding a gazillion new pages to an otherwise small website and wanting to get them indexed sooner or later.  But that's really the only one I can think of.

I'd like to rekindle this discussion two years later.

What if you basically just have a contact page for each location that has the exact same form, but it has a different phone number, address, and embedded map (all with schema markup.)  ?

Let's say you have 5 locations but expect to grow to 15 eventually.  I don't think it's good to junk up your primary navigation dropdown with a list of all these cities.  Seems you could list all the cities (separated by commas in the footer.  OR, what about just a "locations" link in the footer?  The main contact page has a toll free number so there's no need to drive people to the location contact pages, but I would expect it can help local seo a bit to have them indexed?

As usual with most discussion regarding sitemap, you will see 99% of people recommending them provide not concrete, fact based reason as to any actual benefit it provides.

• It provides no SEO advantage

• The reason that it's useful to users is like saying my primary navigation system and search function is too difficult to use.

• If you have a large website with lots of deep, frequently changing content, Google will recognize this and increase the crawl frequency and depth.

Sitemaps in my opinion or for the "tin foil hat" crowd.

But.. conversely, they don't hurt either.  If you have a plugin or script that automatically runs over and over to update it for you, then one could legitimately say "Why not?"

There are some obscure reasons one might use - like adding a gazillion new pages to an otherwise small website and wanting to get them indexed sooner or later.  But that's really the only one I can think of.