Manipulating JSON in Angular - json

Question

Objective: I am trying to build a website URL by concatenating a variety of variables. I get some from JSON file (audience, country, language) + using constants (baseUrl, tailUrl) + some logic applied to an attribute from JSON file (subdir)
Struggle: I have a service that's getting objects from a JSON and then those objects are being used within the app. My original struggle was to map an object from an array to something else (solved using map and switch/case and that worked fine for an array). However, I am having trouble using the map function with these JSON objects.
So in the .html, I am able to loop through the JSON objects just fine, like so:
`
<table class="table table-striped">
<thead>
<tr>
<th>Audience</th>
<th>Country</th>
<th>Language</th>
<th>URL</th>
</tr>
</thead>
<tbody>
<tr *ngFor="let i of siteUrl; let b =index">
<td>{{i.audience}}</td>
<td>{{i.country}}</td>
<td>{{i.language}}</td>
<td>{{(baseUrl)+(i.audience+"/")+(i.country+"/")+(i.language+"/")+(tailUrl)}}</td>
</tr>
</tbody>
</table>
`
However, when I try to do map the objects from the service, I am unable to do so
`
ngOnInit(){
{
this.baseUrl=baseUrlConst;
this.tailUrl=urlTailConst;
this.siteService=smap.map(item =>{
switch (item.audience) {
case 'ABC':
item.audiencesubdir = 'DEF';
break;
case 'UVW':
item.audiencesubdir = 'XYZ';
}
})
}
}
`
I tried arrays instead of JSON and that works fine, but the objects in the JSON itself don't like this function. My understanding of Angular is novice.