diff --git a/.gitignore b/.gitignore
index 24f75cb..f8fec0a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -35,6 +35,7 @@ _*.c
 *.shp
 *.shx
 *.tif
+*.vrt
 *.zarr
 # Logs and databases #
 ######################
diff --git a/IS2view/api.py b/IS2view/api.py
index 5cd1ec3..ce17e77 100644
--- a/IS2view/api.py
+++ b/IS2view/api.py
@@ -1,7 +1,7 @@
 #!/usr/bin/env python
 u"""
 api.py
-Written by Tyler Sutterley (04/2024)
+Written by Tyler Sutterley (06/2024)
 Plotting tools for visualizing rioxarray variables on leaflet maps
 
 PYTHON DEPENDENCIES:
@@ -28,6 +28,7 @@
         https://xyzservices.readthedocs.io/en/stable/
 
 UPDATE HISTORY:
+    Updated 06/2024: use wrapper to importlib for optional dependencies
     Updated 04/2024: add connections and functions for changing variables
         and other attributes of the leaflet map visualization
         simplify and generalize mapping between observables and functionals
@@ -56,20 +57,21 @@
 import collections.abc
 from traitlets import HasTraits, Float, Tuple, observe
 from traitlets.utils.bunch import Bunch
+from IS2view.utilities import import_dependency
 
 # attempt imports
-try:
-    import geopandas as gpd
-except (AttributeError, ImportError, ModuleNotFoundError) as exc:
-    logging.debug("geopandas not available")
-try:
-    import ipywidgets
-except (AttributeError, ImportError, ModuleNotFoundError) as exc:
-    logging.debug("ipywidgets not available")
-try:
-    import ipyleaflet
-except (AttributeError, ImportError, ModuleNotFoundError) as exc:
-    logging.debug("ipyleaflet not available")
+gpd = import_dependency('geopandas')
+ipywidgets = import_dependency('ipywidgets')
+ipyleaflet = import_dependency('ipyleaflet')
+owslib = import_dependency('owslib')
+owslib.wms = import_dependency('owslib.wms')
+rio = import_dependency('rasterio')
+rio.transform = import_dependency('rasterio.transform')
+rio.warp = import_dependency('rasterio.warp')
+xr = import_dependency('xarray')
+xyzservices = import_dependency('xyzservices')
+
+# attempt matplotlib imports
 try:
     import matplotlib
     import matplotlib.cm as cm
@@ -81,23 +83,6 @@
     matplotlib.rcParams['mathtext.default'] = 'regular'
 except (AttributeError, ImportError, ModuleNotFoundError) as exc:
     logging.critical("matplotlib not available")
-try:
-    import owslib.wms
-except (AttributeError, ImportError, ModuleNotFoundError) as exc:
-    logging.debug("owslib not available")
-try:
-    import rasterio.transform
-    import rasterio.warp
-except (AttributeError, ImportError, ModuleNotFoundError) as exc:
-    logging.critical("rasterio not available")
-try:
-    import xarray as xr
-except (AttributeError, ImportError, ModuleNotFoundError) as exc:
-    logging.critical("xarray not available")
-try:
-    import xyzservices
-except (AttributeError, ImportError, ModuleNotFoundError) as exc:
-    logging.debug("xyzservices not available")
 
 # set environmental variable for anonymous s3 access
 os.environ['AWS_NO_SIGN_REQUEST'] = 'YES'
@@ -230,6 +215,8 @@ def _tile_provider(provider):
 
 # create traitlets of basemap providers
 basemaps = _load_dict(providers)
+# set default map dimensions
+_default_layout = ipywidgets.Layout(width='70%', height='600px')
 
 # draw ipyleaflet map
 class Leaflet:
@@ -241,6 +228,8 @@ class Leaflet:
         ``ipyleaflet.Map``
     basemap : obj or NoneType
         Basemap for the ``ipyleaflet.Map``
+    layout : obj, default ``ipywidgets.Layout(width='70%', height='600px')``
+        Layout for the ``ipyleaflet.Map``
     attribution : bool, default False
         Include layer attributes on leaflet map
     scale_control : bool, default False
@@ -280,6 +269,7 @@ class Leaflet:
     def __init__(self, projection, **kwargs):
         # set default keyword arguments
         kwargs.setdefault('map', None)
+        kwargs.setdefault('layout', _default_layout)
         kwargs.setdefault('attribution', False)
         kwargs.setdefault('full_screen_control', False)
         kwargs.setdefault('scale_control', False)
@@ -300,7 +290,9 @@ def __init__(self, projection, **kwargs):
                 zoom=kwargs['zoom'], max_zoom=5,
                 attribution_control=kwargs['attribution'],
                 basemap=kwargs['basemap'],
-                crs=projections['EPSG:3413'])
+                crs=projections['EPSG:3413'],
+                layout=kwargs['layout']
+            )
             self.crs = 'EPSG:3413'
         elif (projection == 'South'):
             kwargs.setdefault('basemap',
@@ -310,7 +302,9 @@ def __init__(self, projection, **kwargs):
                 zoom=kwargs['zoom'], max_zoom=5,
                 attribution_control=kwargs['attribution'],
                 basemap=kwargs['basemap'],
-                crs=projections['EPSG:3031'])
+                crs=projections['EPSG:3031'],
+                layout=kwargs['layout']
+            )
             self.crs = 'EPSG:3031'
         else:
             # use a predefined ipyleaflet map
@@ -508,7 +502,7 @@ def plot_basemap(self, ax=None, **kwargs):
         ax: obj, default None
             Figure axis
         kwargs: dict, default {}
-            Additional keyword arguments for ``wms.getmap``
+            Additional keyword arguments for ``owslib.wms.getmap``
         """
         # set default keyword arguments
         kwargs.setdefault('layers', ['BlueMarble_NextGeneration'])
@@ -777,12 +771,8 @@ def plot(self, m, **kwargs):
         # reduce to variable and lag
         self._variable = copy.copy(kwargs['variable'])
         self.lag = int(kwargs['lag'])
-        if (self._ds[self._variable].ndim == 3) and ('time' in self._ds[self._variable].dims):
-            self._ds_selected = self._ds[self._variable].sel(time=self._ds.time[self.lag])
-        elif (self._ds[self._variable].ndim == 3) and ('band' in self._ds[self._variable].dims):
-            self._ds_selected = self._ds[self._variable].sel(band=1)
-        else:
-            self._ds_selected = self._ds[self._variable]
+        # select data variable
+        self.set_dataset()
         # get the normalization bounds
         self.get_norm_bounds(**kwargs)
         # create matplotlib normalization
@@ -911,7 +901,7 @@ def get_bounds(self):
         """get the bounds of the leaflet map in geographical coordinates
         """
         self.get_bbox()
-        lon, lat = rasterio.warp.transform(
+        lon, lat = rio.warp.transform(
             self.crs['name'], 'EPSG:4326',
             [self.sw['x'], self.ne['x']],
             [self.sw['y'], self.ne['y']])
@@ -1000,7 +990,7 @@ def clip_image(self, ds):
         # attempt to get the coordinate reference system of the dataset
         self.get_crs()
         # convert map bounds to coordinate reference system of image
-        minx, miny, maxx, maxy = rasterio.warp.transform_bounds(
+        minx, miny, maxx, maxy = rio.warp.transform_bounds(
             self.crs['name'], self._ds.rio.crs,
             self.sw['x'], self.sw['y'],
             self.ne['x'], self.ne['y'])
@@ -1023,14 +1013,14 @@ def clip_image(self, ds):
             # warp image to map bounds and resolution
             # input and output affine transformations
             src_transform = ds.rio.transform()
-            dst_transform = rasterio.transform.from_origin(minx, maxy,
+            dst_transform = rio.transform.from_origin(minx, maxy,
                 self.resolution, self.resolution)
             # allocate for output warped image
             dst_width = int((maxx - minx)//self.resolution)
             dst_height = int((maxy - miny)//self.resolution)
             dst_data = np.zeros((dst_height, dst_width), dtype=ds.dtype.type)
             # warp image to output resolution
-            rasterio.warp.reproject(source=ds.values, destination=dst_data,
+            rio.warp.reproject(source=ds.values, destination=dst_data,
                 src_transform=src_transform,
                 src_crs=self._ds.rio.crs,
                 src_nodata=np.nan,
@@ -1148,14 +1138,10 @@ def set_observables(self, widget, **kwargs):
                 except (AttributeError, NameError, ValueError) as exc:
                     pass
 
-    def set_variable(self, sender):
-        """update the dataframe variable for a new selected variable
+    def set_dataset(self):
+        """Select the dataset for the selected variable
+        and time lag
         """
-        # only update variable if a new final
-        if isinstance(sender['new'], str):
-            self._variable = sender['new']
-        else:
-            return
         # reduce to variable and lag
         if (self._ds[self._variable].ndim == 3) and ('time' in self._ds[self._variable].dims):
             self._ds_selected = self._ds[self._variable].sel(time=self._ds.time[self.lag])
@@ -1163,6 +1149,17 @@ def set_variable(self, sender):
             self._ds_selected = self._ds[self._variable].sel(band=1)
         else:
             self._ds_selected = self._ds[self._variable]
+
+    def set_variable(self, sender):
+        """update the plotted variable
+        """
+        # only update variable if a new final
+        if isinstance(sender['new'], str):
+            self._variable = sender['new']
+        else:
+            return
+        # reduce to variable and lag
+        self.set_dataset()
         # check if dynamic normalization is enabled
         if self._dynamic:
             self.get_norm_bounds()
@@ -1263,7 +1260,7 @@ def handle_click(self, **kwargs):
         else:
             self._ds.rio.set_crs(crs)
         # get the clicked point in dataset coordinate reference system
-        x, y = rasterio.warp.transform('EPSG:4326', crs, [lon], [lat])
+        x, y = rio.warp.transform('EPSG:4326', crs, [lon], [lat])
         # find nearest point in dataset
         self._data = self._ds_selected.sel(x=x, y=y, method='nearest').values[0]
         self._units = self._ds[self._variable].attrs['units']
@@ -1575,7 +1572,7 @@ def point(self, ax, **kwargs):
         """
         # convert point to dataset coordinate reference system
         lon, lat = self.geometry['coordinates']
-        x, y = rasterio.warp.transform(self.crs, self._ds.rio.crs, [lon], [lat])
+        x, y = rio.warp.transform(self.crs, self._ds.rio.crs, [lon], [lat])
         # output time series for point
         self._data = np.zeros_like(self._ds.time)
         # reduce dataset to geometry
@@ -1629,7 +1626,7 @@ def transect(self, ax, **kwargs):
         """
         # convert linestring to dataset coordinate reference system
         lon, lat = np.transpose(self.geometry['coordinates'])
-        x, y = rasterio.warp.transform(self.crs, self._ds.rio.crs, lon, lat)
+        x, y = rio.warp.transform(self.crs, self._ds.rio.crs, lon, lat)
         # get coordinates of each grid cell
         gridx, gridy = np.meshgrid(self._ds.x, self._ds.y)
         # clip ice area to geometry
@@ -1997,7 +1994,7 @@ def transect(self, ax, **kwargs):
         """
         # convert linestring to dataset coordinate reference system
         lon, lat = np.transpose(self.geometry['coordinates'])
-        x, y = rasterio.warp.transform(self.crs, self._ds.rio.crs, lon, lat)
+        x, y = rio.warp.transform(self.crs, self._ds.rio.crs, lon, lat)
         # get coordinates of each grid cell
         gridx, gridy = np.meshgrid(self._ds.x, self._ds.y)
         # clip variable to geometry and create mask
diff --git a/IS2view/convert.py b/IS2view/convert.py
index 6cabea9..cb7f8d2 100644
--- a/IS2view/convert.py
+++ b/IS2view/convert.py
@@ -1,6 +1,6 @@
 """
 convert.py
-Written by Tyler Sutterley (08/2023)
+Written by Tyler Sutterley (06/2024)
 Utilities for converting gridded ICESat-2 files from native netCDF4
 
 PYTHON DEPENDENCIES:
@@ -13,6 +13,7 @@
         https://docs.xarray.dev/en/stable/
 
 UPDATE HISTORY:
+    Updated 06/2024: use wrapper to importlib for optional dependencies
     Updated 08/2023: use h5netcdf as the netCDF4 driver for xarray
     Updated 07/2023: use logging instead of warnings for import attempts
     Updated 06/2023: using pathlib to define and expand paths
@@ -23,16 +24,11 @@
 import logging
 import pathlib
 import numpy as np
+from IS2view.utilities import import_dependency
 
 # attempt imports
-try:
-    import h5netcdf
-except (AttributeError, ImportError, ModuleNotFoundError) as exc:
-    logging.critical("h5netcdf not available")
-try:
-    import xarray as xr
-except (AttributeError, ImportError, ModuleNotFoundError) as exc:
-    logging.critical("xarray not available")
+h5netcdf = import_dependency('h5netcdf')
+xr = import_dependency('xarray')
 
 # default groups to skip
 _default_skip_groups = ('METADATA', 'orbit_info', 'quality_assessment',)
diff --git a/IS2view/io.py b/IS2view/io.py
index 00808c3..0159518 100644
--- a/IS2view/io.py
+++ b/IS2view/io.py
@@ -1,6 +1,6 @@
 """
 io.py
-Written by Tyler Sutterley (10/2023)
+Written by Tyler Sutterley (06/2024)
 Utilities for reading gridded ICESat-2 files using rasterio and xarray
 
 PYTHON DEPENDENCIES:
@@ -18,6 +18,7 @@
         https://docs.xarray.dev/en/stable/
 
 UPDATE HISTORY:
+    Updated 06/2024: use wrapper to importlib for optional dependencies
     Updated 10/2023: use dask.delayed to read multiple files in parallel
     Updated 08/2023: use xarray h5netcdf to read files streaming from s3
         add open_dataset function for opening multiple granules
@@ -27,22 +28,13 @@
 """
 from __future__ import annotations
 import os
-import logging
+from IS2view.utilities import import_dependency
 
 # attempt imports
-try:
-    import rioxarray
-    import rioxarray.merge
-except (AttributeError, ImportError, ModuleNotFoundError) as exc:
-    logging.critical("rioxarray not available")
-try:
-    import dask
-except (AttributeError, ImportError, ModuleNotFoundError) as exc:
-    logging.critical("dask not available")
-try:
-    import xarray as xr
-except (AttributeError, ImportError, ModuleNotFoundError) as exc:
-    logging.critical("xarray not available")
+rioxarray = import_dependency('rioxarray')
+rioxarray.merge = import_dependency('rioxarray.merge')
+dask = import_dependency('dask')
+xr = import_dependency('xarray')
 
 # set environmental variable for anonymous s3 access
 os.environ['AWS_NO_SIGN_REQUEST'] = 'YES'
diff --git a/IS2view/tools.py b/IS2view/tools.py
index 8e2c89a..0379538 100644
--- a/IS2view/tools.py
+++ b/IS2view/tools.py
@@ -15,6 +15,7 @@
         https://github.com/matplotlib/matplotlib
 
 UPDATE HISTORY:
+    Updated 06/2024: use wrapper to importlib for optional dependencies
     Updated 11/2023: set time steps using decimal years rather than lags
         setting dynamic colormap with float64 min and max
     Updated 08/2023: added options for ATL14/15 Release-03 data
@@ -28,16 +29,11 @@
 import copy
 import logging
 import numpy as np
+from IS2view.utilities import import_dependency
 
 # attempt imports
-try:
-    import ipywidgets
-except (AttributeError, ImportError, ModuleNotFoundError) as exc:
-    logging.debug("ipywidgets not available")
-try:
-    import matplotlib.cm as cm
-except (AttributeError, ImportError, ModuleNotFoundError) as exc:
-    logging.debug("matplotlib not available")
+ipywidgets = import_dependency('ipywidgets')
+cm = import_dependency('matplotlib.cm')
 
 # set environmental variable for anonymous s3 access
 os.environ['AWS_NO_SIGN_REQUEST'] = 'YES'
@@ -82,15 +78,16 @@ def __init__(self, **kwargs):
         self.directory.layout.display = 'none'
 
         # dropdown menu for setting ATL14/15 release
-        release_list = ['001', '002', '003']
+        release_list = ['001', '002', '003', '004']
         self.release = ipywidgets.Dropdown(
             options=release_list,
-            value='003',
+            value='004',
             description='Release:',
             description_tooltip=("Release: ATL14/15 data release\n\t"
                 "001: Release-01\n\t"
                 "002: Release-02\n\t"
-                "003: Release-03"),
+                "003: Release-03\n\t"
+                "004: Release-04"),
             disabled=False,
             style=self.style,
         )
@@ -166,7 +163,7 @@ def __init__(self, **kwargs):
             style=self.style,
         )
 
-        # dropdown menu for selecting time lag to draw on map
+        # slider for selecting time lag to draw on map
         self.timelag = ipywidgets.IntSlider(
             description='Lag:',
             description_tooltip="Lag: time lag to draw on leaflet map",
@@ -174,7 +171,7 @@ def __init__(self, **kwargs):
             style=self.style,
         )
 
-        # dropdown menu for selecting time step to draw on map
+        # slider for selecting time step to draw on map
         self.timestep = ipywidgets.FloatSlider(
             description='Time:',
             description_tooltip="Time: time step to draw on leaflet map",
@@ -182,6 +179,7 @@ def __init__(self, **kwargs):
             readout=True,
             readout_format='.2f',
             disabled=False,
+            continuous_update=False,
             style=self.style,
         )
 
@@ -381,7 +379,7 @@ def set_atl15_defaults(self, *args, **kwargs):
         # set default variable for group
         self.variable.value = variables[group]
 
-    def set_groups(self, sender):
+    def set_groups(self, *args):
         """sets the list of available groups for a release
         """
         group_list = ['delta_h', 'dhdt_lag1', 'dhdt_lag4', 'dhdt_lag8']
@@ -423,11 +421,11 @@ def set_groups(self, sender):
         self.region.description_tooltip = description_tooltip
 
     def set_variables(self, *args):
-        """sets the list of available variables in a group
+        """sets the list of available variables
         """
-        if any(args):
+        if isinstance(self.data_vars, list):
             # set list of available variables
-            self.variable.options = sorted(args[0].keys())
+            self.variable.options = sorted(self.data_vars)
         else:
             # return to temporary defaults
             self.variable.options = ['delta_h', 'dhdt']
@@ -448,13 +446,32 @@ def set_dynamic(self, *args, **kwargs):
             self.range.value = [-5, 5]
             self.range.layout.display = 'inline-flex'
 
-    def set_time_steps(self, ds, epoch=2018.0):
+    def get_variables(self, d):
+        """
+        Gets the available variables and time steps
+        
+        Parameters
+        ----------
+        d : xarray.Dataset
+            xarray.Dataset object
+        """
+        # data and time variables
+        self.data_vars = sorted(d.data_vars)
+        self.time_vars = d.time.values if 'time' in d else None
+        # set the default groups
+        self.set_groups()
+        # set the default variables
+        self.set_variables()
+        # set the default time steps
+        self.set_time_steps()
+        
+    def set_time_steps(self, *args, epoch=2018.0):
         """sets available time range
         """
         # try setting the min and max time step
         try:
             # convert time to units
-            self.time = list(epoch + ds.time.values/365.25)
+            self.time = list(epoch + self.time_vars/365.25)
             self.timestep.max = self.time[-1]
             self.timestep.min = self.time[0]
             self.timestep.value = self.time[0]
diff --git a/IS2view/utilities.py b/IS2view/utilities.py
index 3f342d4..2bfd69f 100644
--- a/IS2view/utilities.py
+++ b/IS2view/utilities.py
@@ -1,10 +1,17 @@
 #!/usr/bin/env python
 u"""
 utilities.py
-Written by Tyler Sutterley (11/2023)
+Written by Tyler Sutterley (05/2024)
 Download and management utilities
 
+PYTHON DEPENDENCIES:
+    boto3: Amazon Web Services (AWS) SDK for Python
+        https://boto3.amazonaws.com/v1/documentation/api/latest/index.html
+    s3fs: FUSE-based file system backed by Amazon S3
+        https://s3fs.readthedocs.io/en/latest/
+
 UPDATE HISTORY:
+    Updated 05/2024: add wrapper to importlib for optional dependencies
     Updated 11/2023: updated ssl context to fix deprecation error
     Updated 10/2023: filter CMR request type using regular expressions
     Updated 08/2023: added ATL14/15 Release-03 data products
@@ -36,6 +43,7 @@
 import pathlib
 import builtins
 import warnings
+import importlib
 import posixpath
 import traceback
 import subprocess
@@ -49,16 +57,6 @@
     from urllib.parse import urlencode
     import urllib.request as urllib2
 
-# attempt imports
-try:
-    import boto3
-except (AttributeError, ImportError, ModuleNotFoundError) as exc:
-    logging.debug("boto3 not available")
-try:
-    import s3fs
-except (AttributeError, ImportError, ModuleNotFoundError) as exc:
-    logging.debug("s3fs not available")
-
 # PURPOSE: get absolute path within a package from a relative path
 def get_data_path(relpath: list | str | pathlib.Path):
     """
@@ -78,6 +76,47 @@ def get_data_path(relpath: list | str | pathlib.Path):
     elif isinstance(relpath, (str, pathlib.Path)):
         return filepath.joinpath(relpath)
 
+def import_dependency(
+        name: str,
+        extra: str = "",
+        raise_exception: bool = False
+    ):
+    """
+    Import an optional dependency
+    
+    Adapted from ``pandas.compat._optional::import_optional_dependency``
+
+    Parameters
+    ----------
+    name: str
+        Module name
+    extra: str, default ""
+        Additional text to include in the ``ImportError`` message
+    raise_exception: bool, default False
+        Raise an ``ImportError`` if the module is not found
+
+    Returns
+    -------
+    module: obj
+        Imported module
+    """
+    # check if the module name is a string
+    msg = f"Invalid module name: '{name}'; must be a string"
+    assert isinstance(name, str), msg
+    # default error if module cannot be imported
+    err = f"Missing optional dependency '{name}'. {extra}"
+    module = type('module', (), {})
+    # try to import the module
+    try:
+        module = importlib.import_module(name)
+    except (ImportError, ModuleNotFoundError) as exc:
+        if raise_exception:
+            raise ImportError(err) from exc
+        else:
+            logging.debug(err)
+    # return the module
+    return module
+
 # PURPOSE: get the hash value of a file
 def get_hash(
         local: str | io.IOBase | pathlib.Path,
@@ -265,6 +304,7 @@ def s3_client(
     response = urllib2.urlopen(request, timeout=timeout)
     cumulus = json.loads(response.read())
     # get AWS client object
+    boto3 = import_dependency('boto3')
     client = boto3.client('s3',
         aws_access_key_id=cumulus['accessKeyId'],
         aws_secret_access_key=cumulus['secretAccessKey'],
@@ -301,6 +341,7 @@ def s3_filesystem(
     response = urllib2.urlopen(request, timeout=timeout)
     cumulus = json.loads(response.read())
     # get AWS file system session object
+    s3fs = import_dependency('s3fs')
     session = s3fs.S3FileSystem(anon=False,
         key=cumulus['accessKeyId'],
         secret=cumulus['secretAccessKey'],
@@ -405,6 +446,7 @@ def generate_presigned_url(
         s3 presigned https url
     """
     # generate a presigned URL for S3 object
+    boto3 = import_dependency('boto3')
     s3 = boto3.client('s3')
     try:
         response = s3.generate_presigned_url('get_object',
@@ -1218,7 +1260,7 @@ def query_resources(**kwargs):
 
         - ``ATL14`` : land ice height
         - ``ATL15`` : land ice height change
-    release: str, default '001'
+    release: str, default '004'
         ICESat-2 data release
     version: str, default '01'
         ICESat-2 data version
@@ -1256,7 +1298,7 @@ def query_resources(**kwargs):
     kwargs.setdefault('bucket', 'is2view')
     kwargs.setdefault('directory', None)
     kwargs.setdefault('product', 'ATL15')
-    kwargs.setdefault('release', '003')
+    kwargs.setdefault('release', '004')
     kwargs.setdefault('version', '01')
     kwargs.setdefault('cycles', None)
     kwargs.setdefault('region', 'AA')
@@ -1294,7 +1336,7 @@ def query_resources(**kwargs):
     # verify inputs
     assert kwargs['asset'] in _assets
     assert kwargs['product'] in _products
-    assert kwargs['release'] in ('001', '002', '003')
+    assert kwargs['release'] in ('001', '002', '003', '004')
     if kwargs['cycles'] is not None:
         assert (len(kwargs['cycles']) == 2), 'cycles should be length 2'
     for r in kwargs['region']:
@@ -1392,6 +1434,7 @@ def query_resources(**kwargs):
             cycles['001'] = (3, 11)
             cycles['002'] = (3, 14)
             cycles['003'] = (3, 18)
+            cycles['004'] = (3, 21)
             kwargs['cycles'] = cycles[kwargs['release']]
         # for each requested region
         for region in kwargs['region']:
diff --git a/doc/environment.yml b/doc/environment.yml
index 0a1b843..fe70dac 100644
--- a/doc/environment.yml
+++ b/doc/environment.yml
@@ -2,7 +2,7 @@ name: is2view-docs
 channels:
   - conda-forge
 dependencies:
-  - docutils<0.18
+  - docutils
   - graphviz
   - ipywidgets
   - notebook
diff --git a/doc/source/conf.py b/doc/source/conf.py
index 88e1588..076a5de 100644
--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -14,19 +14,18 @@
 # import sys
 import datetime
 # sys.path.insert(0, os.path.abspath('.'))
-from pkg_resources import get_distribution
+import importlib.metadata
 
-
-# -- Project information -----------------------------------------------------
-
-project = 'IS2view'
+# package metadata
+metadata = importlib.metadata.metadata("IS2view")
+project = metadata["Name"]
 year = datetime.date.today().year
 copyright = f"2022\u2013{year}, Tyler C. Sutterley"
-author = 'Tyler Sutterley'
+author = 'Tyler C. Sutterley'
 
 # The full version, including alpha/beta/rc tags
 # get semantic version from setuptools-scm
-version = get_distribution("IS2view").version
+version = metadata["version"]
 # append "v" before the version
 release = f"v{version}"
 
diff --git a/doc/source/release_notes/release-v0.0.9.rst b/doc/source/release_notes/release-v0.0.9.rst
new file mode 100644
index 0000000..10516af
--- /dev/null
+++ b/doc/source/release_notes/release-v0.0.9.rst
@@ -0,0 +1,10 @@
+##################
+`Release v0.0.9`__
+##################
+
+* ``refactor``: simplify and generalize mapping between observables and functionals (`#42 <https://github.com/tsutterley/IS2view/pull/42>`_)
+* ``feat``: minor updates for R004 (`#43 <https://github.com/tsutterley/IS2view/pull/43>`_)
+* ``docs``: bump ``docutils`` (`#43 <https://github.com/tsutterley/IS2view/pull/43>`_)
+* ``docs``: use ``importlib`` rather than ``pkg_resources`` (`#43 <https://github.com/tsutterley/IS2view/pull/43>`_)
+
+.. __: https://github.com/tsutterley/IS2view/releases/tag/0.0.9
diff --git a/doc/source/user_guide/Recipes.rst b/doc/source/user_guide/Recipes.rst
index f00c54a..cc55ff1 100644
--- a/doc/source/user_guide/Recipes.rst
+++ b/doc/source/user_guide/Recipes.rst
@@ -195,3 +195,10 @@ Requires optional ``geopandas`` and ``owslib`` dependencies.
 .. figure:: ../_assets/map.png
    :width: 600
    :align: center
+
+Remove Image Service Layer from Map
+###################################
+
+.. code-block:: python
+
+   ds.leaflet.reset()
diff --git a/notebooks/IS2-ATL14-Viewer.ipynb b/notebooks/IS2-ATL14-Viewer.ipynb
index e06f2e1..5982313 100644
--- a/notebooks/IS2-ATL14-Viewer.ipynb
+++ b/notebooks/IS2-ATL14-Viewer.ipynb
@@ -29,7 +29,7 @@
     "#### Set parameters for ATL14\n",
     "- Asset: Location to get the data\n",
     "- Directory: Working data directory\n",
-    "- Release: ATL14 data release (001, 002, 003)\n",
+    "- Release: ATL14 data release (001, 002, 003, 004)\n",
     "- Region: ATL14 data region (AA, A1, A2, A3, A4, CN, CS, GL, IS, RA, SV)\n",
     "- Format: ATL14 data format to read (nc, zarr)"
    ]
@@ -182,23 +182,6 @@
     "        variable=IS2widgets.variable.value,\n",
     "    )"
    ]
-  },
-  {
-   "attachments": {},
-   "cell_type": "markdown",
-   "metadata": {},
-   "source": [
-    "### Remove the image service layer from the map"
-   ]
-  },
-  {
-   "cell_type": "code",
-   "execution_count": null,
-   "metadata": {},
-   "outputs": [],
-   "source": [
-    "ds.leaflet.reset()"
-   ]
   }
  ],
  "metadata": {
diff --git a/notebooks/IS2-ATL15-Viewer.ipynb b/notebooks/IS2-ATL15-Viewer.ipynb
index 5a9a2a8..f6713d3 100644
--- a/notebooks/IS2-ATL15-Viewer.ipynb
+++ b/notebooks/IS2-ATL15-Viewer.ipynb
@@ -29,7 +29,7 @@
     "#### Set parameters for ATL15\n",
     "- Asset: Location to get the data\n",
     "- Directory: Working data directory\n",
-    "- Release: ATL15 data release (001, 002, 003)\n",
+    "- Release: ATL15 data release (001, 002, 003, 004)\n",
     "- Region: ATL15 data region (AA, A1, A2, A3, A4, CN, CS, GL, IS, RA, SV)\n",
     "- Resolution: ATL15 horizontal resolution (01km, 10km, 20km, 40km)\n",
     "- Group: ATL15 data group to read from file\n",
@@ -129,9 +129,8 @@
     "    draw_control=True,\n",
     "    attribution=False)\n",
     "# set plot attributes\n",
-    "IS2widgets.set_variables(ds)\n",
+    "IS2widgets.get_variables(ds)\n",
     "IS2widgets.set_atl15_defaults()\n",
-    "IS2widgets.set_time_steps(ds)\n",
     "wbox = IS2widgets.VBox([\n",
     "    IS2widgets.variable,\n",
     "    IS2widgets.timestep,\n",
@@ -160,6 +159,7 @@
    "source": [
     "ds.leaflet.plot(m.map, lag=IS2widgets.lag,\n",
     "    vmin=IS2widgets.vmin, vmax=IS2widgets.vmax,\n",
+    "    group=IS2widgets.group.value,\n",
     "    variable=IS2widgets.variable.value,\n",
     "    cmap=IS2widgets.colormap,\n",
     "    opacity=0.75,\n",
@@ -192,21 +192,9 @@
    ]
   },
   {
-   "attachments": {},
    "cell_type": "markdown",
    "metadata": {},
-   "source": [
-    "### Remove the image service layer from the map"
-   ]
-  },
-  {
-   "cell_type": "code",
-   "execution_count": null,
-   "metadata": {},
-   "outputs": [],
-   "source": [
-    "ds.leaflet.reset()"
-   ]
+   "source": []
   }
  ],
  "metadata": {
diff --git a/version.txt b/version.txt
index d169b2f..c5d54ec 100644
--- a/version.txt
+++ b/version.txt
@@ -1 +1 @@
-0.0.8
+0.0.9