diff --git a/render/container.go b/render/container.go
index 82f054f28..53162c2ef 100644
--- a/render/container.go
+++ b/render/container.go
@@ -255,10 +255,10 @@ func MapContainer2IP(m report.Node) []string {
 // format for a container, but without any Major or Minor labels.
 // It does not have enough info to do that, and the resulting graph
 // must be merged with a container graph to get that info.
-func MapProcess2Container(n report.Node) report.Nodes {
+func MapProcess2Container(n report.Node) report.Node {
 	// Propagate pseudo nodes
 	if n.Topology == Pseudo {
-		return report.Nodes{n.ID: n}
+		return n
 	}
 
 	// Otherwise, if the process is not in a container, group it into
@@ -275,7 +275,7 @@ func MapProcess2Container(n report.Node) report.Nodes {
 		id = MakePseudoNodeID(UncontainedID, hostID)
 		node = NewDerivedPseudoNode(id, n)
 	}
-	return report.Nodes{id: node}
+	return node
 }
 
 // MapContainer2ContainerImage maps container Nodes to container
@@ -290,17 +290,17 @@ func MapProcess2Container(n report.Node) report.Nodes {
 // format for a container image, but without any Major or Minor
 // labels.  It does not have enough info to do that, and the resulting
 // graph must be merged with a container image graph to get that info.
-func MapContainer2ContainerImage(n report.Node) report.Nodes {
+func MapContainer2ContainerImage(n report.Node) report.Node {
 	// Propagate all pseudo nodes
 	if n.Topology == Pseudo {
-		return report.Nodes{n.ID: n}
+		return n
 	}
 
 	// Otherwise, if some some reason the container doesn't have a image_id
 	// (maybe slightly out of sync reports), just drop it
 	imageID, ok := n.Latest.Lookup(docker.ImageID)
 	if !ok {
-		return report.Nodes{}
+		return report.Node{}
 	}
 
 	// Add container id key to the counters, which will later be
@@ -308,50 +308,50 @@ func MapContainer2ContainerImage(n report.Node) report.Nodes {
 	id := report.MakeContainerImageNodeID(imageID)
 	result := NewDerivedNode(id, n).WithTopology(report.ContainerImage)
 	result.Counters = result.Counters.Add(n.Topology, 1)
-	return report.Nodes{id: result}
+	return result
 }
 
 // MapContainerImage2Name ignores image versions
-func MapContainerImage2Name(n report.Node) report.Nodes {
+func MapContainerImage2Name(n report.Node) report.Node {
 	// Propagate all pseudo nodes
 	if n.Topology == Pseudo {
-		return report.Nodes{n.ID: n}
+		return n
 	}
 
 	imageName, ok := n.Latest.Lookup(docker.ImageName)
 	if !ok {
-		return report.Nodes{}
+		return report.Node{}
 	}
 
 	imageNameWithoutVersion := docker.ImageNameWithoutVersion(imageName)
 	n.ID = report.MakeContainerImageNodeID(imageNameWithoutVersion)
 
-	return report.Nodes{n.ID: n}
+	return n
 }
 
 var containerHostnameTopology = MakeGroupNodeTopology(report.Container, docker.ContainerHostname)
 
 // MapContainer2Hostname maps container Nodes to 'hostname' renderabled nodes..
-func MapContainer2Hostname(n report.Node) report.Nodes {
+func MapContainer2Hostname(n report.Node) report.Node {
 	// Propagate all pseudo nodes
 	if n.Topology == Pseudo {
-		return report.Nodes{n.ID: n}
+		return n
 	}
 
 	// Otherwise, if some some reason the container doesn't have a hostname
 	// (maybe slightly out of sync reports), just drop it
 	id, ok := n.Latest.Lookup(docker.ContainerHostname)
 	if !ok {
-		return report.Nodes{}
+		return report.Node{}
 	}
 
 	node := NewDerivedNode(id, n).WithTopology(containerHostnameTopology)
 	node.Counters = node.Counters.Add(n.Topology, 1)
-	return report.Nodes{id: node}
+	return node
 }
 
 // MapToEmpty removes all the attributes, children, etc, of a node. Useful when
 // we just want to count the presence of nodes.
-func MapToEmpty(n report.Node) report.Nodes {
-	return report.Nodes{n.ID: report.MakeNode(n.ID).WithTopology(n.Topology)}
+func MapToEmpty(n report.Node) report.Node {
+	return report.MakeNode(n.ID).WithTopology(n.Topology)
 }
diff --git a/render/container_test.go b/render/container_test.go
index f1ce74a1d..f9565b997 100644
--- a/render/container_test.go
+++ b/render/container_test.go
@@ -43,7 +43,7 @@ type testcase struct {
 }
 
 func testMap(t *testing.T, f render.MapFunc, input testcase) {
-	if have := f(input.n); input.ok != (len(have) > 0) {
+	if have := f(input.n); input.ok != (have.ID != "") {
 		name := input.name
 		if name == "" {
 			name = fmt.Sprintf("%v", input.n)
diff --git a/render/render.go b/render/render.go
index ff4e57924..9e944ad8e 100644
--- a/render/render.go
+++ b/render/render.go
@@ -5,10 +5,10 @@ import (
 )
 
 // MapFunc is anything which can take an arbitrary Node and
-// return a set of other Nodes.
+// return another Node.
 //
-// If the output is empty, the node shall be omitted from the rendered topology.
-type MapFunc func(report.Node) report.Nodes
+// If the output ID is blank, the node shall be omitted from the rendered topology.
+type MapFunc func(report.Node) report.Node
 
 // Renderer is something that can render a report to a set of Nodes.
 type Renderer interface {
@@ -107,7 +107,8 @@ func (m Map) Render(rpt report.Report) Nodes {
 
 	// Rewrite all the nodes according to the map function
 	for _, inRenderable := range input.Nodes {
-		for _, outRenderable := range m.MapFunc(inRenderable) {
+		outRenderable := m.MapFunc(inRenderable)
+		if outRenderable.ID != "" {
 			if existing, ok := output[outRenderable.ID]; ok {
 				outRenderable = outRenderable.Merge(existing)
 			}
diff --git a/render/render_test.go b/render/render_test.go
index f2c9a86fc..faf24e419 100644
--- a/render/render_test.go
+++ b/render/render_test.go
@@ -36,8 +36,8 @@ func TestReduceRender(t *testing.T) {
 func TestMapRender1(t *testing.T) {
 	// 1. Check when we return false, the node gets filtered out
 	mapper := render.Map{
-		MapFunc: func(nodes report.Node) report.Nodes {
-			return report.Nodes{}
+		MapFunc: func(nodes report.Node) report.Node {
+			return report.Node{}
 		},
 		Renderer: mockRenderer{Nodes: report.Nodes{
 			"foo": report.MakeNode("foo"),
@@ -53,10 +53,8 @@ func TestMapRender1(t *testing.T) {
 func TestMapRender2(t *testing.T) {
 	// 2. Check we can remap two nodes into one
 	mapper := render.Map{
-		MapFunc: func(nodes report.Node) report.Nodes {
-			return report.Nodes{
-				"bar": report.MakeNode("bar"),
-			}
+		MapFunc: func(nodes report.Node) report.Node {
+			return report.MakeNode("bar")
 		},
 		Renderer: mockRenderer{Nodes: report.Nodes{
 			"foo": report.MakeNode("foo"),
@@ -75,9 +73,9 @@ func TestMapRender2(t *testing.T) {
 func TestMapRender3(t *testing.T) {
 	// 3. Check we can remap adjacencies
 	mapper := render.Map{
-		MapFunc: func(nodes report.Node) report.Nodes {
+		MapFunc: func(nodes report.Node) report.Node {
 			id := "_" + nodes.ID
-			return report.Nodes{id: report.MakeNode(id)}
+			return report.MakeNode(id)
 		},
 		Renderer: mockRenderer{Nodes: report.Nodes{
 			"foo": report.MakeNode("foo").WithAdjacent("baz"),
diff --git a/render/weave.go b/render/weave.go
index 34551e217..a26b4df67 100644
--- a/render/weave.go
+++ b/render/weave.go
@@ -14,10 +14,10 @@ var WeaveRenderer = MakeMap(
 )
 
 // MapWeaveIdentity maps an overlay topology node to a weave topology node.
-func MapWeaveIdentity(m report.Node) report.Nodes {
+func MapWeaveIdentity(m report.Node) report.Node {
 	peerPrefix, _ := report.ParseOverlayNodeID(m.ID)
 	if peerPrefix != report.WeaveOverlayPeerPrefix {
-		return nil
+		return report.Node{}
 	}
 
 	var (
@@ -33,5 +33,5 @@ func MapWeaveIdentity(m report.Node) report.Nodes {
 		node = NewDerivedPseudoNode(id, m)
 	}
 
-	return report.Nodes{node.ID: node}
+	return node
 }