Avoid redundant mappings for C++ program

This is my C++ code which is meant to do the following:

1. Compare a set of XML files and see what is different between them
2. Dump out the node if it is new (in B.xml but not A.xml)
3. Scan that node and associate tags to types of information using map
4. Do work on the data depending on what type it is

I'm pretty happy with how steps 1-2 work but 3-4 I feel I may have implemented poorly. Any help would be appreciated. My main concern is I have to map the tag even if if already matches, such as the id, when really it would be good to define a map only if it's different such as description.

My code:

#include "pugi/pugixml.hpp"

#include <iostream>
#include <string>
#include <map>

int main()
 {
    // This map relates the type of content to the tag name in the XML file
    const std::map<std::string, std::string> tagMap {
         {"id", "id"}, {"description", "content"}, {"url", "web_address"}, {"location", "location"}
     };

    pugi::xml_document doca, docb;
     std::map<std::string, pugi::xml_node> mapa, mapb;

    for (auto& node: doca.child("data").children("entry")) {
     const char* id = node.child_value("id");
     mapa[id] = node;
     }

    for (auto& node: docb.child("data").children("entry")) {
     const char* idcs = node.child_value("id");
         if (!mapa.erase(idcs)) {
         mapb[idcs] = node;
         }
     }

    // For added nodes
     for (auto& eb: mapb) {
         // Loop through Tag map to see if we can find tags named "id, content, web_address or location" in the node returned
         for (auto& kv : tagMap) {
         // For each result, assign the value of that tag to the type of content
         // For example: description = Testing!
         kv.first = eb.second.child_value(kv.second.c_str());
         // If it's an ID...
             if (kv.first == "id") {
             // Do work on ID value (i.e check if it's unique)
             }
             if (kv.first == "description") {
            // Do work on Description data (I.e Trim it)
             }
             if (kv.first == "url") {
             // Do work on URL data (I.e validate it)
             }
             if (kv.first == "location") {
             // Do work on location data
             }
         }
     }

}

Example input file:

<data>
    <entry>
        <id>1</id>
        <content>Description</content>
        <web_address>http://ift.tt/1yK4hfs;
        <location>England</location>
        <unrelated>Test</unrelated>
        <not_needed>Test</not_needed>
    </entry>
..
</data>