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In the present work we investigate variations of ionospheric total electron content (TEC) with applying empirical orthogonal functions (EOF) to the dataset from the global ionospheric maps (GIMs) produced by Jet Propulsion Laboratory (JPL) over two concerned areas: the North America (25-60°N,140-50°W) and East Asia (40-55°N,60-150°E).The results present the common feature in that the first order EOF mode for both areas represent a latitude dependence with semiannual variation strongly modulated by the solar activity.The second order EOF mode exhibit pronounced east-west longitude difference with annual variation moderately in association with solar activity.The third order EOF modes demonstrate possibly a latitudinal dependence influenced by geomagnetic inclination and thermospheric meridional wind.The results reveal the discrepancy of two regions mentioned above in that semiannual variation in the East Asia is more pronounced and possibly controlled by different mechanisms of different latitude bands.Meanwhile,the proportion of east-west difference in the total variance is less evident than that at North America.The annual variation of the nighttime east-west difference is also different.Through statistical analysis the paper improve our current understanding of ionospheric longitude difference at midlatitude.