Custom Rule Engine in WPF - MVVM

using System.Collections.Generic;
using System.Windows.Input;
using CustomRulesMVVM.Models;

namespace CustomRulesMVVM.ViewModels
{
    class CityViewModel:BaseViewModel 
    {
        #region Members
        private const string CITY = "CITY";
        private City _city = new City();
        private RelayCommand _searchCity;
        private string _searchCityResult;
        Dictionary<string, object> collection = new Dictionary<string, object>();
        #endregion

        #region Properties
        /// <summary>
        /// Cityname entered by user
        /// </summary>
        public string CityName
        {
            get { return this._city.CityName; }
            set
            {
                this._city.CityName = value;
                base.OnProperyChanged("CityName");
            }
        }
        /// <summary>
        /// Temperatue entered by user
        /// </summary>
        public string Temperature
        {
            get { return this._city.Temperature; }
            set
            {
                this._city.Temperature = value;
                base.OnProperyChanged("Temperature");
            }
        }
        /// <summary>
        /// Result of city search
        /// </summary>
        public string SearchCityResult
        {
            get { return this._searchCityResult; }
            set
            {
                this._searchCityResult = value;
                base.OnProperyChanged("SearchCityResult");
            }
        }
        /// <summary>
        /// Command for searching city name and temperature
        /// </summary>
        public ICommand SearchCity
        {
            get
            {
                if (null == this._searchCity)
                {
                    this._searchCity = new RelayCommand(param => this.SearchCityDetails());
                }
                return this._searchCity;
            }
        }
        #endregion

        #region Private Methods
        /// <summary>
        /// Searching city details by populating custom rules for this screen and evaluating by passing City object
        /// </summary>
        private void SearchCityDetails()
        {
            //Clear the result 
            this.SearchCityResult = string.Empty;
            //Populate custom rules applicable for this screen by passing the ScreenID (here ScreenID = 2)
            this.PopulateCustomRules(2);
            this.collection[CITY] = _city;
            //Evaluate the rules for City screen            
            this.SearchCityResult = EvaluateCustomRules(collection);
        }     
        #endregion
    }
}