refactor: extract inline type definitions

CONTRIBUTING.md

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+# Contributing to `@openstapps/core`
+
+Please see the appropriate general group contributing guides in [project-management](https://gitlab.com/openstapps/projectmanagement/tree/master/project-docs/workflow).
+
+## Additional coding style
+
+### Extract inline type definitions 
+
+For consistency and correct functionality of `core-tools` we need well-defined type assignments. 
+
+Type assignments shall always be primitive types, classes, interfaces, enums or unions. Not allowed are inline type-definitions. Those shall be refactored accordingly:
+
+```typescript
+export interface SCPlaceWithoutReferences extends SCThing {
+    ...
+    // Use this:
+    geo: SCGeoInformation;
+
+    // Instead of:
+    geo: {
+        point: Point,
+        polygon?: Polygon,
+    };
+}
+```
+
+### Reuse the map structure
+
+If you come around a map-like-type use `SCMap<T>`.
+
+```typescript
+// Use this:
+interface AnyClass{
+    inventory: SCMap<number>;
+}
+
+// Instead of:
+interface AnyClass{
+    inventory?: Array<{ key: string, value: number }>;
+}
+// or instead of
+interface AnyClass{
+    inventory?: { [key: string]: number };
+}
+```