diff --git a/packages/backend/README.md b/packages/backend/README.md
index 8f48979..b07ba02 100644
--- a/packages/backend/README.md
+++ b/packages/backend/README.md
@@ -65,3 +65,7 @@ embedding-atlas path_to_dataset.parquet --x projection_x --y projection_y --neig
 
 The `neighbors` column should have values in the following format: `{"ids": [id1, id2, ...], "distances": [d1, d2, ...]}`.
 If this column is specified, you'll be able to see nearest neighbors for a selected point in the tool.
+
+## Local Development
+
+Launch Embedding Altas with a wine reviews dataset with `./start.sh` and the MNIST dataset with `./start_image.sh`.
diff --git a/packages/viewer/README.md b/packages/viewer/README.md
index 147dd13..24dfc1f 100644
--- a/packages/viewer/README.md
+++ b/packages/viewer/README.md
@@ -13,3 +13,5 @@ Start development server:
 ```bash
 npm run dev
 ```
+
+This will serve Embedding Atlas UI at http://localhost:5173. Note that the UI requires a backend server to provide data to it. You can start one via the `./start.sh` mentioned above. Without a backend server, you can still go to http://localhost:5173/#/test to view a test dataset.
diff --git a/packages/viewer/src/EmbeddingAtlas.svelte b/packages/viewer/src/EmbeddingAtlas.svelte
index b5e3c4b..e34aba7 100644
--- a/packages/viewer/src/EmbeddingAtlas.svelte
+++ b/packages/viewer/src/EmbeddingAtlas.svelte
@@ -20,6 +20,7 @@
   import Spinner from "./widgets/Spinner.svelte";
 
   import {
+    IconClose,
     IconDarkMode,
     IconDashboardLayout,
     IconDownload,
@@ -370,19 +371,60 @@
           {/if}
         </div>
         <!-- Right side -->
-        <div class="flex flex-none gap-2 items-center">
+        <div
+          class="flex flex-none gap-2 items-center pl-2 rounded-md border border-slate-300 dark:border-slate-600 bg-white dark:bg-slate-900"
+        >
           <FilteredCount coordinator={coordinator} filter={crossFilter} table={data.table} />
-          <div class="flex flex-row gap-1 items-center">
+          <div class="flex flex-row items-center">
             <button
-              class="flex px-2.5 mr-1 select-none items-center justify-center text-slate-500 dark:text-slate-300 rounded-full bg-white dark:bg-slate-900 border border-slate-300 dark:border-slate-600 focus-visible:outline-2 outline-blue-600 -outline-offset-1"
-              onclick={resetFilter}
               title="Clear filters"
+              onclick={resetFilter}
+              class="rounded-md flex select-none items-center p-1.5 text-slate-400 dark:text-slate-500 focus-visible:outline-2 outline-blue-600 -outline-offset-1"
             >
-              Clear
+              <IconClose class="w-5 h-5" />
             </button>
+
+            {#if onExportSelection}
+              <PopupButton title="Export Selection">
+                {#snippet button({ visible, toggle })}
+                  <button
+                    title="Export Selection"
+                    onclick={toggle}
+                    class="rounded-md px-1.5 py-1.5 flex select-none items-center focus-visible:outline-2 outline-blue-600 -outline-offset-1"
+                    class:text-slate-400={!visible}
+                    class:dark:text-slate-500={!visible}
+                  >
+                    <IconExport class="w-5 h-5" />
+                  </button>
+                {/snippet}
+                <div class="min-w-[420px] flex flex-col gap-2">
+                  <div class="flex flex-row gap-2">
+                    <ActionButton
+                      icon={IconExport}
+                      label="Export Selection"
+                      title="Export the selected points"
+                      class="w-48"
+                      onClick={() => onExportSelection(currentPredicate(), exportFormat)}
+                    />
+                    <Select
+                      label="Format"
+                      value={exportFormat}
+                      onChange={(v) => (exportFormat = v)}
+                      options={[
+                        { value: "parquet", label: "Parquet" },
+                        { value: "jsonl", label: "JSONL" },
+                        { value: "json", label: "JSON" },
+                        { value: "csv", label: "CSV" },
+                      ]}
+                    />
+                  </div>
+                </div>
+              </PopupButton>
+            {/if}
           </div>
         </div>
-        <div class="flex flex-none flex-row gap-0.5">
+
+        <div class="flex flex-none flex-row gap-2">
           <div class="grid grid-cols-1 grid-rows-1 justify-items-end items-center">
             {#key layout}
               <div transition:scale class="col-start-1 row-start-1">
@@ -429,41 +471,17 @@
                   }}
                 />
               {/if}
-              <!-- Export -->
-              {#if onExportSelection || onExportApplication}
+              <!-- Export Application -->
+              {#if onExportApplication}
                 <h4 class="text-slate-500 dark:text-slate-400 select-none">Export</h4>
                 <div class="flex flex-col gap-2">
-                  {#if onExportSelection}
-                    <div class="flex flex-row gap-2">
-                      <ActionButton
-                        icon={IconExport}
-                        label="Export Selection"
-                        title="Export the selected points"
-                        class="w-48"
-                        onClick={() => onExportSelection(currentPredicate(), exportFormat)}
-                      />
-                      <Select
-                        label="Format"
-                        value={exportFormat}
-                        onChange={(v) => (exportFormat = v)}
-                        options={[
-                          { value: "parquet", label: "Parquet" },
-                          { value: "jsonl", label: "JSONL" },
-                          { value: "json", label: "JSON" },
-                          { value: "csv", label: "CSV" },
-                        ]}
-                      />
-                    </div>
-                  {/if}
-                  {#if onExportApplication}
-                    <ActionButton
-                      icon={IconDownload}
-                      label="Export Application"
-                      title="Download a self-contained static web application"
-                      class="w-48"
-                      onClick={onExportApplication}
-                    />
-                  {/if}
+                  <ActionButton
+                    icon={IconDownload}
+                    label="Export Application"
+                    title="Download a self-contained static web application"
+                    class="w-48"
+                    onClick={onExportApplication}
+                  />
                 </div>
               {/if}
               <h4 class="text-slate-500 dark:text-slate-400 select-none">About</h4>
diff --git a/packages/viewer/src/app/Test.svelte b/packages/viewer/src/app/Test.svelte
index 8da93a6..6ea0795 100644
--- a/packages/viewer/src/app/Test.svelte
+++ b/packages/viewer/src/app/Test.svelte
@@ -6,11 +6,15 @@
 
   import type { EmbeddingAtlasProps } from "../api.js";
   import { initializeDatabase } from "../utils/database.js";
+  import { downloadBuffer } from "../utils/download.js";
+  import { exportMosaicSelection, type ExportFormat } from "../utils/mosaic_exporter.js";
   import type { DataSource } from "./data_source.js";
 
   export class TestDataSource implements DataSource {
     private count: number;
 
+    downloadSelection: ((predicate: string | null, format: ExportFormat) => Promise<void>) | undefined = undefined;
+
     constructor(count: number) {
       this.count = count;
     }
@@ -55,6 +59,11 @@
         UPDATE ${table} SET y = y + 5 * floor(floor(var_uniform * 24 + random()) / 5);
       `);
 
+      this.downloadSelection = async (predicate, format) => {
+        let [bytes, name] = await exportMosaicSelection(coordinator, table, predicate, format);
+        downloadBuffer(bytes, name);
+      };
+
       return {
         data: {
           table: table,
diff --git a/packages/viewer/src/widgets/PopupButton.svelte b/packages/viewer/src/widgets/PopupButton.svelte
index f2b09b5..367e6d9 100644
--- a/packages/viewer/src/widgets/PopupButton.svelte
+++ b/packages/viewer/src/widgets/PopupButton.svelte
@@ -11,12 +11,17 @@
     label?: string | null;
     icon?: any | null;
     anchor?: "left" | "right";
+    button?: Snippet<[{ visible: boolean; toggle: () => void }]>;
     children?: Snippet;
   }
 
-  let { title = "", label = null, icon = null, anchor = "right", children }: Props = $props();
+  let { title = "", label = null, icon = null, anchor = "right", children, button }: Props = $props();
 
   let visible: boolean = $state(false);
+
+  function toggle() {
+    visible = !visible;
+  }
   let container: HTMLDivElement;
 
   function onKeyDown(e: KeyboardEvent) {
@@ -50,7 +55,11 @@
 
 <!-- svelte-ignore a11y_no_static_element_interactions -->
 <div class="relative" bind:this={container} onkeydown={onKeyDown}>
-  <ToggleButton icon={icon} title={title} label={label} bind:checked={visible} />
+  {#if button}
+    {@render button({ visible, toggle })}
+  {:else}
+    <ToggleButton icon={icon} title={title} label={label} bind:checked={visible} />
+  {/if}
   <div
     bind:this={popoverElement}
     class="absolute px-3 py-3 rounded-md z-20 bg-slate-100 dark:bg-slate-800 border border-slate-300 dark:border-slate-700 shadow-lg"