readme for data

README_data.md

+Data Description
+================
+
+Geopackages here contain:
+
+* Tables called `level_N` where `N` is the Uber H3 Hex resolution. These
+are geopackage polygon layers.
+
+These can be read with `sf::st_read`:
+
+```
+u1 = st_read("./hexes/inst/data/uk_hex_1_6.gpkg","level_1")
+```
+
+* Tables called `adjlevel_N` where `N` is the Uber H3 Hex resolution. These
+have two columns, `i` and `j`, showing adjacency between row `i` and
+row `j` in the corresponding `level_N` table. There are no self-adjacencies
+in this table, and hexes that have no neighbours do not appear.
+
+These can be read with the `DBI` and `RSQLite` packages:
+
+```
+> con = dbConnect(SQLite(), "./hexes/inst/data/uk_hex_1_6.gpkg")
+> adj1 = dbReadTable(con,"adjlevel_1")
+> dim(adj1)
+[1] 14  2
+```
+