label-scaling.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE Map[]>
<Map srs="+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over" buffer-size="128">

<Parameters>
  <Parameter name="bounds">-120.0146,27.6057,-104.6118,36.0313</Parameter>
  <Parameter name="center">-113.4888,32.38,6</Parameter>
</Parameters>


<Style name="label" filter-mode="first">
  <Rule>
    <TextSymbolizer face-name="Arial Unicode MS Regular" size="12" horizontal-alignment="middle" dx="-5" ><![CDATA[[name]]]></TextSymbolizer>
  </Rule>
</Style>
<Layer name="label"
  srs="+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs">
    <StyleName>label-fill</StyleName>
    <StyleName>label</StyleName>
    <Datasource>
       <Parameter name="file"><![CDATA[label.json]]></Parameter>
       <Parameter name="layer"><![CDATA[OGRGeoJSON]]></Parameter>
    </Datasource>
  </Layer>

</Map>

label.json

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "geometry": {
        "type": "Polygon",
        "coordinates": [
          [
            [
              -114.60088875,
              32.5482997332272
            ],
            [
              -111.94219734375,
              32.5482997332272
            ],
            [
              -111.94219734375,
              32.2923383967611
            ],
            [
              -114.60088875,
              32.2923383967611
            ],
            [
              -114.60088875,
              32.5482997332272
            ]
          ]
        ]
      },
      "properties": {
        "name": "San Luis Río Colorado"
      }
    }
  ]
}