PyPSA-eur/Clustering.md

 ## Different number of nodes in countries
+* use pypsa-eur config.yaml
+* calculate focus weights:
+1. For example, you want all countries with one node except for Germany, here you want 10 nodes.
+2. Pypsa-eur usually looks at 33 countries. So in total, you want 43 nodes.
+3. Germany gets a focus weight of 10/43.
+4. All other countries get a focus weight of 1/43.
+* add focus weights in the form of:
+
+`focus weights: `
+
+ ` 'DE': 0.2326 `
+
+ ` 'IT': 0.02326 `
+`...`
+
+* all countries must have a focus weight
+* the total number of nodes for this case is **47**, because there are four countries, who always have two nodes: Great Britain (Northern Ireland and the rest), Italy (mainland Italy and Sardinia), Denmark (the part, which borders Germany, and the part, which borders Sweden) and Spain (mainland Spain and balearic islands). Therefore, the minmum number of nodes possible is 37 and not 33 (= number of countries). For the calulation of focus weights, those extra nodes must not be paid attention to. 
+* When you want to have a higher nodal resolution of one of these four countries, maybe some adjustments must be made
 
 ## Custom Clustering
 This page was written and tested for the commit 03221fe539bf9f24806a96c0939aa34b05e5f4cc (21.10.2020) on the [custom_busmap_for_clustering](https://github.com/PyPSA/pypsa-eur/tree/custom_busmap_for_clustering) branch of the [PyPSA-eur repository](https://github.com/PyPSA/pypsa-eur).