Michal Zimmermann Pieces of knowledge from the world of GIS.

Plotting the Czech Cadastre Land Use with d3: Data Extraction (part I)

Written on Nov 13, 2016 and marked as javascript, d3, postgresql, svg | data

This post is the first part of the upcoming series summarizing the process of visualizing landuse data with bash, PostgreSQL and d3.js. Read other parts:

  1. you’re reading it now
  2. Plotting the Czech Cadastre Land Use with d3: Data Transformation (part II)
  3. Plotting the Czech Cadastre Land Use with d3: Data Transformation (part III)

Czech Office for Surveying, Mapping and Cadastre has recently published lot of data via Atom feed. There’s pretty small and a bit boring dataset included, featuring quarterly updated landuse-related values for all 13,091 cadastral areas:

  • absolute number of land lots within given category (arable land, forests, etc.)
  • absolute area of land lots within given category

Data are published as CSV files linked from the Atom feed. Sadly, they come windows-1250 encoded, using Windows line endings, with trailing semicolons and header rows using diacritics.

ETL process

Before the d3 viz can be crafted, it’s necessary to:

  1. extract CSV data from the URLs provided via the Atom feed
  2. transform those data into a relational database, do some math
  3. load data into a d3.js viz
  4. profit (as usual)

Extract

#!/bin/bash
# extract.sh -f YYYYMMDD

while [[ $# -gt 1 ]]
do
key="$1"

case $key in
    -f|--file)
    FILE="$2"
    shift # past argument
    ;;
    *)
        # unknown option
    ;;
esac
shift # past argument or value
done

URL=http://services.cuzk.cz/sestavy/UHDP/UHDP-
CSVFILE=$FILE.csv
CSVUTF8FILE=${CSVFILE%.*}.utf.csv
URL+=$CSVFILE

echo "downloading $URL"
wget -q $URL -O $CSVFILE

if [[ $? != 0 ]]; then
    rm -f $CSVFILE
    echo "download failed"
    exit
fi

echo "converting to utf-8"
iconv -f WINDOWS-1250 -t UTF-8 $CSVFILE -o $CSVUTF8FILE && \
echo "modifying ${FILE}"
sed -i 's/^M$//' $CSVUTF8FILE && \
sed -i 's/\r$//' $CSVUTF8FILE && \
sed -i 's/;*$//g' $CSVUTF8FILE && \
sed -i '1d' $CSVUTF8FILE

echo "importing to database"
sed -e "s/\${DATE}/$FILE/g" extract.sql | psql -qAt --no-psqlrc

rm $CSVFILE $CSVUTF8FILE

This script downloads CSV file, deals with all the pitfalls mentioned above and, when done, copy command within extract.sql loads the data into a data_YYYYMMDD table. Putting all the files into the one table would have saved me a lot of transformation SQL, yet it didn’t feel quite right though.

Transform

See Plotting the Czech Cadastre Land Use with d3: Data Transformation (part II).

Load

See Plotting the Czech Cadastre Land Use with d3: Data Transformation (part III).