diff --git a/src/components/categorical/categorical.js b/src/components/categorical/categorical.js
index 149dab01..aee6604e 100644
--- a/src/components/categorical/categorical.js
+++ b/src/components/categorical/categorical.js
@@ -8,38 +8,49 @@ import SectionHeader from "../framework/sectionHeader"
 import createCategoryCounts from "./createCategoryCounts";
 import { alphabeticallySortedValues } from "./util";
 
+@connect((state) => {
+  return {
+    selectedMetadata: state.selectedMetadata
+  }
+})
 class Button extends React.Component {
   render () {
+
+    /* has this value for this category already been selected? */
+    let fontWeight;
+    if (!this.props.selectedMetadata) { /* there is no selected metadata */
+      fontWeight = 400;
+    } else if (
+      this.props.selectedMetadata[this.props.metadataField] && /* the key {Location: []} is present  */
+      this.props.selectedMetadata[this.props.metadataField].indexOf(this.props.value) > -1 /* "Tumor" exists in {Location: ["Tumor"]}  */
+    ) {
+      fontWeight = 700
+    }
+
     return (
-      <button
+      <div
         key={this.props.i}
-        onClick={this.props.handleClick(this.props.category, this.props.value)}
+        onClick={this.props.handleClick(this.props.metadataField, this.props.value)}
         style={{
-          border: "none",
-          background: "none",
-          color: "black",
-          marginRight: 3,
           cursor: "pointer",
+          display: "flex",
+          fontWeight,
         }}>
-        {this.props.value}
-        <span
-          style={{
-            fontFamily: globals.accentFont,
-            fontStyle: "italic",
-            color: globals.darkGrey,
-            fontSize: globals.tiniestFontSize,
-            marginLeft: 4,
-            position: "relative",
-            top: -1,
+        <div style={{
+            width: 200,
+            flexShrink: 0,
           }}>
+          {this.props.value}
+        </div>
+        <span>
           {this.props.count}
         </span>
-      </button>
+      </div>
     )
   }
 }
 
-const Category = ({category, values, handleClick}) => (
+const Category = ({metadataField, values, handleClick}) => (
   <div style={{
       display: "flex",
       alignItems: "baseline",
@@ -52,7 +63,7 @@ const Category = ({category, values, handleClick}) => (
         fontFamily: globals.accentFont,
         fontStyle: "italic",
         marginRight: 20,
-      }}>{category}:</p>
+      }}>{metadataField}:</p>
     <div>
       {
         _.map(alphabeticallySortedValues(values), (v, i) => {
@@ -60,7 +71,7 @@ const Category = ({category, values, handleClick}) => (
             <Button
               key={v}
               handleClick={handleClick}
-              category={category}
+              metadataField={metadataField}
               count={values[v]}
               value={v}
               i={i} />
@@ -73,17 +84,10 @@ const Category = ({category, values, handleClick}) => (
 
 @connect((state) => {
 
-  let ranges = null;
-
-  if (
-    state.cells.cells &&
-    state.cells.cells.data.ranges
-  ) {
-    ranges = state.cells.cells.data.ranges;
-  }
+  const ranges = state.cells.cells && state.cells.cells.data.ranges ? state.cells.cells.data.ranges : null;
 
   return {
-    ranges: ranges
+    ranges
   }
 })
 class Categories extends React.Component {
@@ -93,9 +97,9 @@ class Categories extends React.Component {
 
     };
   }
-  handleClick(category, value) {
+  handleClick(metadataField, value) {
     return () => {
-      this.props.dispatch({type: "category changed", data: {category, value}})
+      this.props.dispatch({type: "categorical metadata filter selected", metadataField, value})
     }
   }
   render () {
@@ -113,7 +117,7 @@ class Categories extends React.Component {
                 <Category
                   handleClick={this.handleClick.bind(this)}
                   key={key}
-                  category={key}
+                  metadataField={key}
                   values={value.options}/>
               )
             } else {
diff --git a/src/reducers/selectedMetadata.js b/src/reducers/selectedMetadata.js
new file mode 100644
index 00000000..ce135837
--- /dev/null
+++ b/src/reducers/selectedMetadata.js
@@ -0,0 +1,53 @@
+import uri from "urijs";
+import _ from "lodash";
+
+/************************************************************************
+*************************************************************************
+1. This is all of the state that will be stored in the URL query params.
+1a. It is reasonably important it be kept in the same place,
+because if initial load or back button etc, we'll hear about that
+and manually reconstruct the state from the url, overriding whatever
+we had. We could of course listen for the "url changed" type in another
+reducer, if this gets messy.
+1b. The data structures used here are constrained as well, as urijs
+needs to be able to parse them, if arrays: https://hackernoon.com/redux-patterns-add-edit-remove-objects-in-an-array-6ee70cab2456
+*************************************************************************
+************************************************************************/
+
+const selectedMetadata = (
+  state = {},
+  action
+) => {
+  switch (action.type) {
+    case "url changed": {
+      const {url} = action;
+      const parsed = uri.parseQuery(window.location.search);
+      // console.log("onURLchange sees: ", state, parsed)
+      return state;
+    }
+    case "categorical metadata filter selected": {
+      if (!state[action.metadataField]) { /* we don't have the field, which means this is a simple insertion */
+        /* {} becomes {Location: ["Tumor"]} */
+        return Object.assign({}, state, {[action.metadataField]: [action.value]});
+      } else { /* we do have the field, so we need to push to a copy of the array */
+        const updatedField = state[action.metadataField].slice()
+        updatedField.push(action.value)
+        return Object.assign({}, state, {
+          /* {Location: ["Tumor"]} becomes {Location: ["Tumor", "Periphery"]} */
+          [action.metadataField]: updatedField
+        })
+      }
+    }
+    case "categorical metadata filter deselected": {
+      return Object.assign({}, state, {
+
+      })
+    }
+    default:
+      return state;
+  }
+
+  return state;
+}
+
+export default selectedMetadata;
diff --git a/src/reducers/url.js b/src/reducers/url.js
deleted file mode 100644
index a8264b22..00000000
--- a/src/reducers/url.js
+++ /dev/null
@@ -1,43 +0,0 @@
-import uri from "urijs";
-
-/************************************************************************
-*************************************************************************
-1. This is all of the state that will be stored in the URL query params.
-1a. It is reasonably important it be kept in the same place,
-because if initial load or back button etc, we'll hear about that
-and manually reconstruct the state from the url, overriding whatever
-we had. We could of course listen for the "url changed" type in another
-reducer, if this gets messy.
-1b. The data structures used here are constrained as well, as urijs
-needs to be able to parse them
-*************************************************************************
-************************************************************************/
-
-const url = (
-  state = {
-    selectedMetadata: {}
-  },
-  action
-) => {
-  switch (action.type) {
-    case "url changed": {
-      const {url} = action;
-
-      // const parsed = uri.parseQuery(window.location.search);
-
-      // console.log("onURLchange sees: ", state, parsed)
-
-      return state;
-    }
-    case "category changed": {
-
-      return state;
-    }
-    default:
-      return state;
-  }
-
-  return state;
-}
-
-export default url;