diff --git a/docs-src/docs/advanced-functionality/view-settings.md b/docs-src/docs/advanced-functionality/view-settings.md
index 5325225b0..a7b86b997 100644
--- a/docs-src/docs/advanced-functionality/view-settings.md
+++ b/docs-src/docs/advanced-functionality/view-settings.md
@@ -37,6 +37,7 @@ For instance, if you set `display_defaults.color_by` to `country`, but load the
 | `layout`            | Tree layout        | "rect", "radial", "clock" or "unrooted |
 | `branch_label`      | Which set of branch labels are to be displayed | "aa", "lineage" |
 | `panels`            | List of panels which (if available) are to be displayed  | ["tree", "map"] |
+| `transmission_lines`| Should transmission lines (if available) be rendered on the map?  | Boolean |
 
 
 Note that `meta.display_defaults.panels` (optional) differs from `meta.panels` (required), where the latter lists the possible panels that auspice may display for the dataset.
diff --git a/src/actions/recomputeReduxState.js b/src/actions/recomputeReduxState.js
index b69db6c97..274c88152 100644
--- a/src/actions/recomputeReduxState.js
+++ b/src/actions/recomputeReduxState.js
@@ -192,11 +192,11 @@ const modifyStateViaMetadata = (state, metadata) => {
     console.warn("JSON did not include any filters");
   }
   if (metadata.displayDefaults) {
-    const keysToCheckFor = ["geoResolution", "colorBy", "distanceMeasure", "layout", "mapTriplicate", "selectedBranchLabel", 'sidebar'];
-    const expectedTypes =  ["string",        "string",  "string",          "string", "boolean",       "string",              'string']; // eslint-disable-line no-multi-spaces
+    const keysToCheckFor = ["geoResolution", "colorBy", "distanceMeasure", "layout", "mapTriplicate", "selectedBranchLabel", 'sidebar', "showTransmissionLines"];
+    const expectedTypes =  ["string",        "string",  "string",          "string", "boolean",       "string",              'string',  "boolean"              ]; // eslint-disable-line
 
     for (let i = 0; i < keysToCheckFor.length; i += 1) {
-      if (metadata.displayDefaults[keysToCheckFor[i]]) {
+      if (Object.hasOwnProperty.call(metadata.displayDefaults, keysToCheckFor[i])) {
         if (typeof metadata.displayDefaults[keysToCheckFor[i]] === expectedTypes[i]) { // eslint-disable-line valid-typeof
           if (keysToCheckFor[i] === "sidebar") {
             if (metadata.displayDefaults[keysToCheckFor[i]] === "open") {
@@ -631,10 +631,11 @@ const createMetadataStateFromJSON = (json) => {
       map_triplicate: "mapTriplicate",
       layout: "layout",
       sidebar: "sidebar",
-      panels: "panels"
+      panels: "panels",
+      transmission_lines: "showTransmissionLines"
     };
     for (const [jsonKey, auspiceKey] of Object.entries(jsonKeyToAuspiceKey)) {
-      if (json.meta.display_defaults[jsonKey]) {
+      if (Object.prototype.hasOwnProperty.call(json.meta.display_defaults, jsonKey)) {
         metadata.displayDefaults[auspiceKey] = json.meta.display_defaults[jsonKey];
       }
     }
diff --git a/src/components/map/map.js b/src/components/map/map.js
index 2ff7d90a8..3ec2b2c5b 100644
--- a/src/components/map/map.js
+++ b/src/components/map/map.js
@@ -220,6 +220,7 @@ class Map extends React.Component {
         this.props.pieChart,
         this.props.legendValues,
         this.props.colorBy,
+        this.props.showTransmissionLines,
         this.props.dispatch
       );
 
@@ -385,6 +386,7 @@ class Map extends React.Component {
         nextProps.pieChart,
         nextProps.legendValues,
         nextProps.colorBy,
+        nextProps.showTransmissionLines,
         nextProps.dispatch
       );
       const d3elems = drawDemesAndTransmissions(
@@ -397,8 +399,7 @@ class Map extends React.Component {
         nextProps.dateMaxNumeric,
         nextProps.pieChart,
         nextProps.geoResolution,
-        nextProps.dispatch,
-        nextProps.showTransmissionLines
+        nextProps.dispatch
       );
       this.setState({
         d3elems,
diff --git a/src/components/map/mapHelpers.js b/src/components/map/mapHelpers.js
index 23add1ee7..15a46f2ea 100644
--- a/src/components/map/mapHelpers.js
+++ b/src/components/map/mapHelpers.js
@@ -137,8 +137,7 @@ export const drawDemesAndTransmissions = (
   numDateMax,
   pieChart, /* bool */
   geoResolution,
-  dispatch,
-  showTransmissionLines
+  dispatch
 ) => {
 
   // add transmission lines
@@ -165,7 +164,7 @@ export const drawDemesAndTransmissions = (
     .attr("stroke-opacity", 0.6)
     .attr("stroke-linecap", "round")
     .attr("stroke", (d) => { return d.color; })
-    .attr("stroke-width", showTransmissionLines ? 1 : 0);
+    .attr("stroke-width", 1);
 
   const visibleTips = nodes[0].tipCount;
   const demeMultiplier =
diff --git a/src/components/map/mapHelpersLatLong.js b/src/components/map/mapHelpersLatLong.js
index cfb11f1ce..8a213e18b 100644
--- a/src/components/map/mapHelpersLatLong.js
+++ b/src/components/map/mapHelpersLatLong.js
@@ -399,6 +399,7 @@ export const createDemeAndTransmissionData = (
   pieChart,
   legendValues,
   colorBy,
+  showTransmissionLines,
   dispatch
 ) => {
   /*
@@ -414,16 +415,21 @@ export const createDemeAndTransmissionData = (
     demeIndices
   } = setupDemeData(nodes, visibility, geoResolution, nodeColors, triplicate, metadata, map, pieChart, legendValues, colorBy);
 
-  /* second time so that we can get Bezier */
-  const { transmissionData, transmissionIndices, demesMissingLatLongs } = setupTransmissionData(
-    nodes,
-    visibility,
-    geoResolution,
-    nodeColors,
-    triplicate,
-    metadata,
-    map
-  );
+  let transmissionData = [];
+  let transmissionIndices = {};
+  let demesMissingLatLongs = new Set(); // TODO: this won't be filled in if we're not showing transmission lines...
+  if (showTransmissionLines) {
+    /* second time so that we can get Bezier */
+    ({ transmissionData, transmissionIndices, demesMissingLatLongs } = setupTransmissionData(
+      nodes,
+      visibility,
+      geoResolution,
+      nodeColors,
+      triplicate,
+      metadata,
+      map
+    ));
+  }
 
   const filteredDemesMissingLatLongs = [...demesMissingLatLongs].filter((value) => {
     return value.toLowerCase() !== "unknown";