Custom Rule Engine in WPF - MVVM

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

namespace CustomRulesMVVM.ViewModels
{
    class CityStateViewModel:BaseViewModel 
    {
        #region Members
        private const string CITY = "CITY";
        private const string STATE = "STATE";
        private City _city = new City();
        private State _state = new State();
        private RelayCommand _searchCityState;
        private string _searchCityStateResult;
        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 CityTemperature
        {
            get { return this._city.Temperature; }
            set
            {
                this._city.Temperature = value;
                base.OnProperyChanged("CityTemperature");
            }
        }
        /// <summary>
        /// Cityname entered by user
        /// </summary>
        public string StateName
        {
            get { return this._state.StateName; }
            set
            {
                this._state.StateName = value;
                base.OnProperyChanged("StateName");
            }
        }
        /// <summary>
        /// Temperatue entered by user
        /// </summary>
        public string StateTemperature
        {
            get { return this._state.Temperature; }
            set
            {
                this._state.Temperature = value;
                base.OnProperyChanged("StateTemperature");
            }
        }
        /// <summary>
        /// Result of city & state search
        /// </summary>
        public string SearchCityStateResult
        {
            get { return this._searchCityStateResult; }
            set
            {
                this._searchCityStateResult = value;
                base.OnProperyChanged("SearchCityStateResult");
            }
        }
        /// <summary>
        /// Command for searching city name and temperature OR state name and temperature
        /// </summary>
        public ICommand SearchCityState
        {
            get
            {
                if (null == this._searchCityState)
                {
                    this._searchCityState = new RelayCommand(param => this.SearchCityStateDetails());
                }
                return this._searchCityState;
            }
        }
        #endregion

        #region Private Methods
        /// <summary>
        /// Searching city details & state details by populating custom rules for this screen and evaluating by passing City & State object
        /// </summary>
        private void SearchCityStateDetails()
        {
            //Clear the result 
            this.SearchCityStateResult = string.Empty;
            //Populate custom rules applicable for this screen by passing the ScreenID (here ScreenID = 3)
            this.PopulateCustomRules(3);
            this.collection[CITY] = _city;
            this.collection[STATE] = _state;
            //Evaluate the rules for City screen            
            this.SearchCityStateResult = EvaluateCustomRules(collection);
        }

        #endregion
    }
}