diff --git a/.spyproject/config/backups/workspace.ini.bak b/.spyproject/config/backups/workspace.ini.bak
index 609b183915f88e7154837370361124c1f9c01767..ce680e7203aeca3171d4da30488f0380274aaf8d 100644
--- a/.spyproject/config/backups/workspace.ini.bak
+++ b/.spyproject/config/backups/workspace.ini.bak
@@ -4,7 +4,7 @@ save_data_on_exit = True
 save_history = True
 save_non_project_files = False
 project_type = empty-project-type
-recent_files = ['../clumpy-cases/simple_case/run_raw.py', 'clumpy/calibration/_calibrator.py', 'clumpy/_base/_land.py', 'clumpy/allocation/_allocator.py', 'clumpy/allocation/_unbiased.py', 'clumpy/allocation/_unbiased_mono_pixel.py', 'clumpy/feature_selection/_mRMR.py']
+recent_files = ['../clumpy-cases/simple_case/run_raw.py', 'clumpy/calibration/_calibrator.py', 'clumpy/layer/_layer.py', 'clumpy/layer/_land_use_layer.py', 'clumpy/map/_land_use_map.py', 'clumpy/map/_map.py', 'clumpy/__init__.py', 'clumpy/map/__init__.py', 'requirements.txt']
 
 [main]
 version = 0.2.0
diff --git a/.spyproject/config/workspace.ini b/.spyproject/config/workspace.ini
index 55339f74077977b5d24c9ed36010970174737561..ce680e7203aeca3171d4da30488f0380274aaf8d 100644
--- a/.spyproject/config/workspace.ini
+++ b/.spyproject/config/workspace.ini
@@ -4,7 +4,7 @@ save_data_on_exit = True
 save_history = True
 save_non_project_files = False
 project_type = empty-project-type
-recent_files = ['../clumpy-cases/simple_case/run_raw.py', 'clumpy/calibration/_calibrator.py', 'clumpy/layer/_layer.py', 'clumpy/layer/_land_use_layer.py', 'clumpy/map/_land_use_map.py', 'clumpy/map/_map.py', 'clumpy/__init__.py', 'clumpy/map/__init__.py']
+recent_files = ['../clumpy-cases/simple_case/run_raw.py', 'clumpy/calibration/_calibrator.py', 'clumpy/layer/_layer.py', 'clumpy/layer/_land_use_layer.py', 'clumpy/map/_land_use_map.py', 'clumpy/map/_map.py', 'clumpy/__init__.py', 'clumpy/map/__init__.py', 'requirements.txt']
 
 [main]
 version = 0.2.0
diff --git a/README.md b/README.md
index b6a082d194d539358701783640926f3b6eab1c5f..e985ba2d1d73966b47418370a2adb4cbd61eb052 100644
--- a/README.md
+++ b/README.md
@@ -20,6 +20,9 @@ François-Rémi Mazy
 
 *The software provided by pip is not up to date !*
 
+Create conda env
+`conda create -n clumpy python=3.8 spyder gdal rasterio`
+
 build the package :
 `python3 setup.py sdist bdist_wheel`
 
diff --git a/clumpy/layer/_layer.py b/clumpy/layer/_layer.py
index a0f8a07ddc93178025976e7226e814845627b2a8..4e808223ce7a29cbca1b672533210faf316622f7 100644
--- a/clumpy/layer/_layer.py
+++ b/clumpy/layer/_layer.py
@@ -13,20 +13,22 @@ logger = logging.getLogger('clumpy')
 
 from ..tools._console import stop_log
 
-class Layer:
+class Layer(np.ndarray):
     """Layer base element
     """
+    
+    def __new__(cls, input_array):
+        obj = np.asarray(input_array).view(cls)
+        return obj
 
     def __init__(self,
                  label=None,
-                 time=0,
                  path=None,
                  data=None,
                  band_tags=None,
                  copy_geo=None):
         
         self.label = label
-        self.time = time
         self.path = path
         self.copy_geo = copy_geo