Custom Shipping Zones makes use of Shopify's real time carrier api allowing for shipping rates to be set at the time the buyer checks out based on the postal / zip code of the order's shipping address. Rates for different postal / zip codes can be set up based on the order weight and/or price.
Standard Shopify shipping functionality generally allows shipping rates to be set down to a province or state level however, depending on the carrier being used, shipping rates can vary significantly within the same province / state. The Custom Shipping Zones app allows shipping rates to be set at a postal / zip code level thereby providing a more granular level of control on what shipping rates are charged to your buyers.
The app has preconfigured custom zones set up for specific countries based on how common carriers / couriers charge for shipments. If definitions for your country do not exist, contact us and we will gladly set them up for you (or you can create your own custom zone definitions by uploading a spreadsheet).
Also, check out the uAfrica Multichannel app for other shipping tools such as tracking for over 300 carriers worldwide and waybill generation.