Topology

Edge flow is affected by the poles contained in a model. A pole is any vertex that has a number of connecting edges different than 4.

When using Subdivision modifier this becomes very apparent and breaks the edge flow.

On edges, bevels and crease can be used to create support topology.

Bevel adds smoother topology at the expense of more vertices.

Crease imitates the presence of supporting loops without adding topology but can create uneven topology if the adjacent edges are not at equal distance from creased edge.

When bridging between two meshes that have different numbers of edges / vertices, to conserve the quad based mesh and avoid n-gons use the knife tool K in a similar fashion:

This also redirects the topology flow in a sort of 180° U-turn.

The second smaller zone is made by insetting the two faces with B for boundaries activated.

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This construction can bring 3 edges to a zone with one edge. Slide the middle edge inward, select the three edges and F to fill then the 1:1 edges and F to fill.

Notice the 180° turn on the edge flow again.

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Keeping quads in the mesh enables a better control over the shape afterwards.

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