# What are the geometric principles and GIS techniques that I can use to generate a postcode coverage of my city at street scales?

Postal codes of Brazil and another countries are oriented to distribution logistics, and improvement of reliability in writing the postal addresses; but without much concern for the spatial correlation.

Old codes, with 5 digits, have good spatial correlations (national scale), but new codes, with 8 digits (street scale), no. It is a situation similar to the USA-zipcode.

So, the problem is: "What are the geometric principles and GIS techniques that I can use to generate a postcode coverage of my city at street scales?"

Important-1: the POSTCODE codes are defined only into a cadastral database, there are no geographical association. Each POSTCODE is associated to an street name, range of house numbers, and number parity.

Important-2: brasilian house-numbers have only 70% to 90% (depends of city) of spatial correlation, that is, 10% to 30% can not be interpolated, because they are "numerological" or not checked with the correct street metrics.

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# NOTES

(these notes are subsidies, not a "complete answer", I need YOUR answer!).

I have something, but no reliable sources/references, neither bether clues or confirmations... Do you have sources?

Geometrical principles:

1. Points with POSTCODE defined: there are two ways to define georrefered points of POSTCODES,

1.1. by postal address: addresses (points) obtained by GPS and/or geocodification.

1.2. by streets: streets (lines) have georeferenced metric and orientation, so they can be linked to the database.

2. Points with POSTCODE nonexistent: points where no house exists. Rivers, lakes, points of intersection of roads, etc.

3. Points without POSTCODE: all other points of the city, where the POSTCODE can be inferred spatially.

4. Through the above definitions, the without POSTCODE points can have your POSTCODE assigned by the following ground rules:

4.1. RULE-1: set to closer with POSTCODE defined point.

4.2. RULE-2: faces of urban blocks are uniform. Into urban blocks areas, definitions 1.1 and 1.2 above must be consistent with each other, so the points of the edges of each side of the urban blocks, all assume the same POSTCODE. We can fill the area by rule-1.

4.3. RULE-3: faces of urban blocks must be splitted into 2 parts when the POSTCODE range (of house numbers) limits lies at some point of the block.

Fundamentals for apply GIS procedures:

• The POSTCODE can be accurately assigned through the "faces of urban blocks", directed the respective streets. (see rule-2).

• Extrapolation of POSTCODE beyond the interior of blocks is provided by the "influence of the closest POSTCODE" that is, by construction of the Voronoi cell/Thiessen coverage.

Theoretical results applying these fundamentals:

An experiment with only Thiessen (+dissolve) coverage by address points, showing the same "lozenge-shape" patterns.

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