I agree with PhiLho.  Although, technically you can make manipulations with without push/popMatrix(), I don't think it's best practice.  Otherwise, all of your changes get compounded upon one another and it's very difficult to parse out what's happening where.  Definitely read up on it if you haven't already. 

I don't have your images so I couldn't get it to work exactly how you'd like.  However, I was able to make a sketch where there are two stick figures where one gets bigger as the other gets smaller.  Hopefully it will work the same way with the image if you uncomment it.  I used the same display function so I didn't include it below, you can just copy and past this on top of it.

For the sake of understanding, comment out all of the push/popMatrix()'s and see what happens.  You'll notice that in this particular instance, it doesn't make an enormous difference but there is a bit.  Since I always use push/pop, I can't speak for how often you can get away with not using them but like I said, it's not a great practice.  Even if you just have a single translation, I think it's a good idea to encase them in a push/popMatrix().

1. color c = color(255);
2. //PImage img;
3. //PShape bot;
4. void setup() {
5.       size(680,510);
6.       background(155);
7. //      img = loadImage("Carretera.jpg");
8. //      bot = loadShape("bot1.svg");
9. }
10. void draw() {
11. //  background(img);
12.   background(155);
13.  
14.   pushMatrix();
15.  
16.     translate(width/2, height/2);
17.    
18.       pushMatrix();
19.          float zoom1 = map(mouseX, 0, width, 0.1, 4.5);
20.             scale(zoom1);
21. //          shape(bot, -140,-140);
22.             display(); //comment this out when you add back in your image.
    
23.       popMatrix();
24.      
25.       pushMatrix();
26.         float zoom = map(mouseX, width, 0, 0.1, 4.5);
27.         scale(zoom);
28.         display();
29.       popMatrix();
30.      
31.   popMatrix();
32. }