# Additional Material on Flows, Networks and Geographic Visualization

For our last course on flows and networks, I have uploaded additional material. Slides are now online

A markdown-based webpage is now online, with all the codes.

# Nodal Regions and Flows

For practicals on networks and flows, we will use the R package flows dedicated to flows on networks

```library(flows) data(nav) myflows <- prepflows(mat = nav, i = "i", j = "j", fij = "fij") diag(myflows) <- 0```

Select flows that represent at least 20% of the sum of outgoing flows for each urban area.

`flowSel1 <- firstflows(mat = myflows/rowSums(myflows)*100, method = "xfirst",k = 20)`

Then select the dominant flows (incoming flows criterion)

```flowSel2 <- domflows(mat = myflows, w = colSums(myflows), k = 1) flowSel <- myflows * flowSel1 * flowSel2 inflows <- data.frame(id = colnames(myflows), w = colSums(myflows))```

and finally plot dominant flows map

```opar <- par(mar = c(0,0,2,0)) sp::plot(GE, col = "#cceae7", border = NA) plotMapDomFlows(mat = flowSel, spdf = UA, spdfid = "ID", w = inflows, wid = "id",wvar = "w", wcex = 0.05, add = TRUE,legend.flows.pos = "topright",legend.flows.title = "Nb. of commuters") title("Dominant Flows of Commuters")```

The code to get the background map is based on the GE object, defined in that package.

To go further on dominant flows read  Nystuen & Dacey (1961)

We will discuss in the last course, next week  two extensions that were not mentioned in the course. The first one is about congestion models. The second one is a nice application of flow to discuss sports issues in NBA (or NHL).

# Introduction to Graphs and Networks

This week, we will start the first graduate course on graphs and networks. Slides are available online.

Later on, we will see additional applications, in the context of flows, matching, transportation, etc.