DVF statistics

Data statistics [DVF](https://www.data.gouv.fr/en/datasets/requests-de-values-foncières/), viewable on the website [explore.data.gouv.fr/real estate](https://explore.data.gouv.fr/real estate). The files contain the number of sales, the average and the median of prices in m². - Total DVF statistics: statistics by geographical scale, over the 10 semesters available. - Monthly DVF statistics: statistics by geographical scale and by month. ## Description of treatment The [code](https://github.com/etalab/datagouvfr _data_pipelines/tree/main/data_processing/dvf) allows to generate statistics from the [data of land value requests](https://files.data.gouv.fr/geo-dvf/latest/csv/), aggregated at different scales, and their evolution over time (monthly). The choice was made to calculate the following indicators on a monthly basis and over the entire period available (10 semesters): * number of mutations * average prices in m² * median prices in m² * distribution of sales prices by tranches for each type of property from: * houses * apartments * houses + apartments * commercial premises and for each scale from: * nation * Department * EPCI * common * cadastral section The source data contain the following types of mutations: sale, sale in the future state of completion, sale of building land, auction, expropriation and exchange. We have chosen to keep only sales, sales in the future state of completion and auctions for statistics*. In addition, for the sake of simplicity, we have chosen to keep only the mutations that concern a single property (without dependence)*. Our path is as follows: 1. for a transfer that would include property of several types (e.g. a house + a commercial space), it is not possible to reconstitute the share of the land value attributed to each of the included property. 2. for a transfer that would include several properties of the same type (e.g. X apartments), the total value of the transfer is not necessarily equal to X times the value of an apartment, especially in the case where the properties are very different (surface, work to be carried out, floor, etc.). We had initially kept these goods by calculating the price at the m² of the transfer by considering the goods of the transfer as a single good from an area to the sum of the surfaces of the goods, but this method, which ultimately concerned only a marginal quantity of goods, did not convince us for the final version. The price per m² is then calculated by dividing the land value of the change by the surface area of the building of the property concerned. Finally, we exclude transfers for which we could not calculate the price per m², as well as those for which the price per m² is more than €100k (arbitrary choice)*. We have not incorporated any further restrictions on outliers in order to maintain fidelity to the original data and to trace potential anomalies. Displaying the median on the site reduces the impact of outliers on color scales. _*: The mentioned filters are applied for the calculation of the statistics, but all the mutations of the source files are well displayed on the application at plot level._