C#

using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Windows.Forms;

namespace YourNameSpace
{
    public partial class AutoNumberedLabel : Label
    {
        public AutoNumberedLabel()
        {
            InitializeComponent();
        }
        
        // this constructor is called when the control is created at run-time
        public AutoNumberedLabel(IContainer container)
        {
            container.Add(this);

            InitializeComponent();

            LabelId = lblId;

            IntToLabel.Add(lblId++, this);
        }

        static Dictionary<int, AutoNumberedLabel> IntToLabel = new Dictionary<int, AutoNumberedLabel>();

        static int lblId = 0;

        public int LabelId { get; }

        public static AutoNumberedLabel GetLabelByID(int id)
        {
            if (IntToLabel.ContainsKey(id))
            {
                return IntToLabel[id];
            }

            throw new KeyNotFoundException();
        }

        public static void SetLabelColorByID(int id, Color color)
        {
            if (IntToLabel.ContainsKey(id))
            {
               IntToLabel[id].BackColor =  color;
               return;
            }

            throw new KeyNotFoundException();
        }
    }
}

private void autoNumberedLabel_Click(object sender, EventArgs e)
{
    AutoNumberedLabel lbl = (AutoNumberedLabel) sender;
    
    int Id = lbl.LabelId;

    // test if a round-trip works
    AutoNumberedLabel lbl2 = AutoNumberedLabel.GetLabelByID(Id);
    if(lbl2 != lbl) throw new ArgumentException();

    AutoNumberedLabel.SetLabelColorByID(Id, Color.Gold);
}

• Add a city
• Add a zone
• Add another zone
• Add another city
• Add a zone
• Edit a city
• Edit a zone.

Rectangle r1 = Screen.PrimaryScreen.Bounds;
Rectangle r2 = this.Bounds;
Rectangle r3 = this.ClientRectangle;
Rectangle r4 = this.DisplayRectangle;

Console.WriteLine($"screen {r1}\nform bounds {r2}\nform displayrect {r3}\nform clientrect {r2}");