title: Keras input explanation: input_shape, units, batch_size, dim, etc
body: <p>For any Keras layer (<code>Layer</code> class), can someone explain how to understand the difference between <code>input_shape</code>, <code>units</code>, <code>dim</code>, etc.?  </p>
  
  <p>For example the doc says <code>units</code> specify the output shape of a layer. </p>
  
  <p>In the image of the neural net below <code>hidden layer1</code> has 4 units. Does this directly translate to the <code>units</code> attribute of the <code>Layer</code> object? Or does <code>units</code> in Keras equal the shape of every weight in the hidden layer times the number of units? </p>
  
  <p>In short how does one understand/visualize the attributes of the model -  in particular the layers - with the image below? 
  <a href="https://i.stack.imgur.com/iHW2o.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/iHW2o.jpg" alt="enter image description here"></a></p>