1\section{Economic interpretation, policy relevance and limitations}\label{sec:discussion}23\subsection{What the online catalogue of a region is}4The results are consistent with a simple reading. Quebec's online retail supply, as seen through an aggregator of independent merchants, is overwhelmingly a population of small catalogues (median 35 listings) dominated in volume by a handful of very large ones. Regional specialization exists at the level of \emph{who} sells online --- maple, cheese and cider producers in some regions, fashion and jewellery designers in Montréal, garden and seed merchants in others --- but once listing volumes are counted, a region's assortment is largely the catalogue of whichever large merchants happen to be located there, and a random relocation of merchants would produce as much apparent specialization. This distinction between merchant-level and listing-level specialization is the paper's main descriptive finding and a caution for any use of catalogue counts as regional indicators. Diversity, measured on an equal footing of fifteen merchants, is narrow in range (0.74--0.85 on a 0--1 scale) and unrelated to regional scale in our data; the hierarchy of city size that structures employment \citep{polese2006,shearmur2007} and business-type diversity \citep{youn2016,hong2020} does not reproduce in the breadth of online assortments of located merchants, although a sample of sixteen regions can only detect large associations. Posted prices of the same product differ across merchants by a median of about five log points, half of the matched groups differ by more than five per cent, and the dispersion is structured both by geography and by channel: resellers and collective storefronts post lower prices than the producers' own shops for the same item, which is the opposite of a retail margin and is consistent with producers using their own shop as a list-price channel while discounting through distributors. Neither mechanism can be identified here.56\subsection{Policy relevance}7Three uses follow, each within the limits of the data. First, for ``buy local'' and regional branding policies, the certification registries and regional agri-food brands that feed the aggregator are themselves the main determinant of which merchants are visible online; a region's online presence is partly a function of its directories. Second, the ECI-type complexity indicators that are increasingly used in regional policy \citep{balland2019} do not survive bootstrap validation on a 17$\times$20 matrix of online categories: a policy indicator built this way would reshuffle regional rankings from one resample of merchants to the next, and we therefore withhold both the complexity component and a composite score. Third, the within-product price dispersion across merchants is large enough to matter for consumers comparing local producers with distributors, and the collection plan in Appendix~\ref{app:prereg} describes how a repeated snapshot with store pinning would turn the cross-section into a price panel.89\subsection{Limitations}10The limitations ledger in the repository lists fifteen items; the five that bound every conclusion are the following. (i) Listings are posted offers of located merchants: nothing here measures production, sales, employment or product origin. (ii) The discovery process is non-probability and region-correlated: coverage per thousand business locations varies six-fold, and 19\% of the assortment sample has no recoverable location. (iii) Category labels are measured with error: the platform's keyword rules reach 46\% precision, the classifier we substitute is validated on an independent audit but trained on model annotations, and all category results are reported under both labellings. (iv) With sixteen or seventeen regions the scale association and the complexity validation have little power, and the region effects in the price regression are identified only through products sold in several regions. (v) The snapshot is a single cross-section without price history; dynamics are confined to ten weeks of listing entry and are exploratory.11