March 7, 2021

Product Categorisation in Ecommerce

Dr Peter Mowforth

With any ecommerce project, sorting out what you are selling into the right categories is a hugely important thing to get right if you want to make your business a success. Let’s start with a bit of theory and then work through the implementation issues.Product Information Architecture (Taxonomy)In 1956, the psychologist George Miller, wrote a classic article titled “The Magical Number Seven, Plus or Minus Two: Some Limits on our Capacity for Processing Information” (ref). The theory is that the number of objects an average human can hold in working memory is 7 ± 2. This has been used to explain much about human behaviour covering everything from how human groups work (from company structures to remembering phone numbers) along with how we understand our perceptions and interact together. Understanding the limits can help optimise everything from restaurant menus through to Government surveys … and, of course, ecommerce website design.Category UsabilityHow quickly and easily customers are able to find the products they want is a key objective when categorising what you are selling. Tools such as Treejack are just one of the ways to help make sure you can shorten the distance to what you are looking for.

Once you have optimised the usability of your category structure, the next step is to implement and test a menu structure that will work across all devices:

The Toolstop desktop site has 8 main categories in the main menu plus a blog link. The Power Tools category is then organised with 6 sub-categories with each of those showing 5 sub-sub categories. The mobile site groups its main categories into 9 main areas.Category Landing Pages and SEOWith ecommerce, most landing pages are either product pages or category pages. Ideal categorisation is where the category aligns perfectly with search volume - i.e. each category targets a particular market niche where there are customers looking to buy things.An important issue with ecommerce websites concerns the number of products on the category pages. An ideal category page has around 50-60 products (around the magic number squared) which seems the best compromise between usability, internal SEO architecture linking and depth within the site (deep pages within a site rank less well). To avoid deep pages that might be difficult for a search engine to spider, well-built ecommerce websites canonicalise multi-page results to a ‘view-all’ page. This means that instead of Google registering a ‘page 1, page 2, etc’ they simply see all the products at the same level. This gives improved internal linking and better SEO results (ref).Standard Categories on Third Party sitesAlmost all ecommerce websites push products to third party sites such as eBay or Amazon. These third party sites often require products to be mapped onto their own categories e.g. here. The more standard you are in the way you structure your products, the easier will be your job when using these third party sites.WarehousingGood ecommerce is about having a joined-up business. This means that the warehouse where storage, pick, pack and despatch takes place are commonly organised in a similar way that they are categorised on the website. Even within a niche category, the default ordering of products that show the most popular items first in the warehouse mean that you can minimise the distance walked for product picking. One INDEZ customer originally organised their warehouse alphabetically. After changing over to adopt a similar structure as used by the website, warehousing operations took a major step forward in productivity.PostscriptThere are clearly common threads around around the principle of the 7 ± 2 (ish) organisational  branching principle. Is this something that’s human-specific or is there some universal principle at work?I wrote this piece at home, where, at the top of our garden we have a few mature trees. I wondered up to take a look and started trying to count the number of main branches that come from the trunk and then the number of secondary branches and so on all the way to the leaves. Being as scientific as possible I estimated that the number of branching steps from the leaves to the trunk were around 7 and that the number of sub-branches from a main branch again was also around 7. This would mean that an average tree might have very roughly 7 to the power 7  (7*7*7*7*7*7*7) leaves - i.e. in the order of 80,000 leaves for a fairly average-to-large mature tree. Googling the results took me to an article from Wired Magazine (here) that comes to a remarkably similar answer but following a completely different analysis. That said, it’s worth noting that we comfortably use words like tree, branch, root etc when talking about anything to do with organisation, categorisation and structure.

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