Blockchain Business Example "Smart Property Contract"

This contract is for tangible and intangible property such as Cars, Houses or Patents.
Can be used to record and verify property rights.

First, payable is a modifier that can be added to a function. It's impossible to have payable() as a function name as it is a reserved keyword. You may use payable only in addition to existing functions 

Second, Payable allows a function to receive ether while being called as stated in docs.It's manadatory from solidity 0.4.x. If you try to send ether using call

pragma solidity ^0.4.18;

contract LandAresh {
    
    address public owner; 
    uint public defaultCost;
    uint public mainLandCost;
   
    mapping(uint => mapping(uint => address))public properties;
    mapping(uint => mapping(uint => address))public landContent;
    mapping(uint => mapping(uint => bool))public status;
    mapping(uint => mapping(uint => uint))public prices;
    
    function LandAresh() public {
        owner = msg.sender;
    }
    //x and y represent the position of the land in a GRID
    function setLandPrice(uint x,uint y,uint price) public
    {
       if(status[x][y])
       {
            if(msg.sender==properties[x][y])
            {
                prices[x][y]=price;
            }
       }
       else
       {
            if(msg.sender==owner)
            {
                prices[x][y]=price;
            }
        }
    }
    
    function setMainLandCost(uint price) public
    {
        if(msg.sender==owner) mainLandCost=price;
    }

    function setDefaultCost(uint price) public 
    {
       if(msg.sender==owner) defaultCost=price;
    }
    
    function getLocation(uint x,uint y)public constant returns(uint,address,bool)
    {
        return(prices[x][y],properties[x][y],status[x][y]); 
    }
    
    function buyMainLand() public payable
    {
        //If bigger than zero, means lang is available
       if(mainLandCost>0)
       {
           if(msg.value>=mainLandCost)
           {
               owner=msg.sender;
               mainLandCost=0;
           }
       }
    }
    
    function buyLand(uint x,uint y)public payable
    {
       if(status[x][y])
       {
           //land has owner
           if(prices[x][y]>0) //if price is not zero then its for sale
           {
               if(msg.value>=prices[x][y]) //sell at higher price
               {
                   properties[x][y]=msg.sender; //sold, assigned owner
               }
           }
       }
       else
       {
           //land has no owner
           if(prices[x][y]>0)
           {
               if(msg.value>=prices[x][y])
               {
                   properties[x][y]=msg.sender;
                   status[x][y]=true;
               }
           }
           if(prices[x][y]==0)
           {
               if(msg.value>=defaultCost)
               {
                   properties[x][y]=msg.sender;
               }
           }
       }
    }
    
    function setLand(uint x,uint y,address entity) public
    {
        if(status[x][y])
        {
            //if status is true, land contains property
            if(properties[x][y]==msg.sender)
            {
                landContent[x][y]=entity;
            }
            else
            {
                revert();
            }
        }
        else
        {
            //land has no property
            if(owner==msg.sender)
            {
                landContent[x][y]=entity;
            }
            else
            {
                revert();
            }
            
        }
    }
}