North of Porto

the Luis I - bridge in Porto 

designed by Théophile Seyrig, a colleague of Gustave Eiffel

North of Porto are many possibilities to follow the way to Santiago de Compostela.
See the possibilities on http://www.caminador.es/wp-content/uploads/2009/06/LLEGAR-EN-AVION.pdf 

You can choose:
1) the Camino de la Costa
2) the Senda (da Orla) Litoral (that follows the coast line)
3) the Camino Central
4) start with the Camino de la Costa and later on take a right turn to the Camino Central
5) start with the Senda (da Orla) Litoral and later on take a right turn to the Camino Central

Watch out:
From Porto through Maia, Vilarinho to Rates you will experience a lot of traffic. You have to walk on the emergency part of the highway and many trucks are passing you. And you will experience then many paths with little cobble stones that are not very comfortable. The best is to walk a part of Senda (da Orla) Litoral that follows the coast line and from Vila do Conde you can go in direction of Rates or ... you can walk the whole coastal road.

I am planning to walk along the coast until Vila do Conde and from there I'll take a right turn to Rates where I will arrive at the Camino Central, the camino with more pilgrims and more camino history. In Vila do Conde I'll cross the bridge over the Rio Ave and I'll take a right turn. Then I'll follow my way to Rates, so that I am heading for the Camino Central in direction of Barcelos. 

See for the map between Vila do Conde and Rates:
http://www.caminador.es/wp-content/uploads/2009/06/9-VILADOCONDE-RATES-guia-2x1B.pdf

You can take even the metro straight from the airport or from the centre of Porto to metro station Santa Clara near the centre of Vila do Conde and start your camino from there. Many pilgrims start their camino from metro station Mercado in Matosinhos and follow the coast (= Senda da Orla Litoral) to scip the busy parts of Porto.
When you are planning to walk the whole coastal road you can even start your camino in Póvoa de Varzim by taking the metro to the end station there. The metro is going far outside the city borders.
See for the map of the metro of the Porto area: http://www.metrodoporto.pt/en/ (and click on the tab "System Map").

From the cathedral of Porto I'll walk into southern direction to the river Douro. Along the river Douro (beautiful + flat) I'll walk in western direction to the coast (probably no pilgrims there!) and I'll continue along the coast line to Matosinhos (= about 12 km from the cathedral) from where I'll take the metro from metro station Mercado back to my hostel in Porto. The other day I'll continue from that metro station Mercado. The first day I'll leave my backpack at my hostel J