What is difference between these two declarations of associative arrays in Bash?

I am playing a bit with associative arrays in Bash and I found the following difference when declaring the exact same associative array with and without declare. The code is as follows:

#!/usr/bin/env bash

echo -e "\n\nASSOCIATIVE ARRAY\n"
declare -A MY_MAP=( 
    [Madrid]="Spanish" 
    [London]="English" 
    [Paris]="French" 
    [1]=2
    [3]=3.14 
)
echo "First element: $MY_MAP"
echo "Whole content as single string: ${MY_MAP[*]}"
echo "Whole content quoted separately: ${MY_MAP[@]}"
echo "List of indices: ${!MY_MAP[@]}"
echo "Array length: ${#MY_MAP[*]}"
echo "Array length: ${#MY_MAP[@]}"
echo "Second element: ${MY_MAP[London]}"
echo "Last 2 elements: ${MY_MAP[@]:1:3}"

echo -e "\n\nASSOCIATIVE ARRAY - 2\n"
MY_MAP2=( 
    [Madrid]="Spanish" 
    [London]="English" 
    [Paris]="French" 
    [1]=2
    [3]=3.14 
)
echo "First element: $MY_MAP2"
echo "Whole content as single string: ${MY_MAP2[*]}"
echo "Whole content quoted separately: ${MY_MAP2[@]}"
echo "List of indices: ${!MY_MAP2[@]}"
echo "Array length: ${#MY_MAP2[*]}"
echo "Array length: ${#MY_MAP2[@]}"
echo "Second element: ${MY_MAP2[London]}"
echo "Last 2 elements: ${MY_MAP2[@]:1:3}"

When I execute the previous script I do get the following output:

ASSOCIATIVE ARRAY

First element: 
Whole content as single string: French 3.14 2 English Spanish
Whole content quoted separately: French 3.14 2 English Spanish
List of indices: Paris 3 1 London Madrid
Array length: 5
Array length: 5
Second element: English
Last 2 elements: French 3.14 2


ASSOCIATIVE ARRAY - 2

First element: French
Whole content as single string: French 2 3.14
Whole content quoted separately: French 2 3.14
List of indices: 0 1 3
Array length: 3
Array length: 3
Second element: French
Last 2 elements: 2 3.14

My question is what is declare -A doing that makes the output different?

A detailed insight of what is happening here will be appreciated.

Thanks a lot in advance.