added in additional details on the kind of data preparation that is b…

…eing undertaken as per #39

data-preparation/JIBE-vis-data-preparation-R.qmd

@@ -77,6 +77,16 @@ No data or data-related outputs will be included in this document or repository.
 
 Note that due to limitations of the Postrion IDA (currently in Beta), large code chunks must be split up in order to note exceed R's internal console buffer size.  So, this will be done below (for example, when defining area data).
 
+## General principles
+
+A number of steps must be undertake for data to be included in the Transport Health Impacts (aka JIBE Vis) platform.  Data should be prepared at the appropriate scales required for visualisation with only the relevant variables that will be used.  Reducing the complexity of data in this way will result in lower file sizes and improved performance when streaming data over the internet and processing it on user's computers (which may be mobile phones, laptops or desktop computers).
+
+In general, data which is to be mapped is required in the Protomaps [pmtiles](https://docs.protomaps.com/pmtiles/) format.  These is a vector map tile format, optimised for streaming complex data at a range of spatial scales for use in interactive map visualisations.  These files will be uploaded to the `tiles` folder in the Transport Health Impacts platform's Amazon Web Services (AWS) S3 storage bucket.
+
+In order to get spatial data into the pmtiles format, the software [Tippecanoe](https://github.com/felt/tippecanoe) is used.  Tippecanoe can convert CSV, Geojson, or ideally Flatgeobuf data into vector map tiles in the required format.  Details on the conversion of source data into the required formats will be included in this document.
+
+Additional data processing and formatting will be undertaken as required, and documented here.
+
 ## Status
 
 14 October 2024: commenced, in progress
@@ -544,7 +554,9 @@ synpop$merged <- synpop$merged %>%
 synpop$merged %>% names()
 ```
 
+#### Prepare Greater Manchester region boundary
 
+The Greater Manchester boundary needs to be extracted from the Ordnance Survey BoundaryLine dataset and saved as